Thursday, July 1, 2010

Arrays and pointers Questions

1. I had the definition char x[6] in one source file, and in another I declared extern char *x. Why didn't it work?

A: The declaration extern char *x simply does not match the actual definition. The type "pointer-to-type-T" is not the same as "array-of-type-T." Use extern char x[].

References: CT&P Sec. 3.3 pp. 33-4, Sec. 4.5 pp. 64-5.

2. But I heard that char x[] was identical to char *x.

A: Not at all. (What you heard has to do with formal parameters to functions; see question 19.) Arrays are not pointers. The array declaration "char a[6];" requests that space for six characters be set aside, to be known by the name "a." That is, there is a location named "a" at which six characters can sit. The pointer declaration "char *p;" on the other hand, requests a place which
holds a pointer. The pointer is to be known by the name "p," and can point to any char (or contiguous array of chars) anywhere.

As usual, a picture is worth a thousand words. The statements
char a[] = "hello";
char *p = "world";

would result in data structures which could be represented like this:
+---+---+---+---+---+---+
a: | h | e | l | l | o |\0 |
+---+---+---+---+---+---+

+-----+ +---+---+---+---+---+---+
p: | *======> | w | o | r | l | d |\0 |
+-----+ +---+---+---+---+---+---+

3. You mean that a reference like x[3] generates different code depending on whether x is an array or a pointer?

A: Precisely. Referring back to the sample declarations in the previous question, when the compiler sees the expression a[3], it emits code to start at the location "a," move three past it, and fetch the character there. When it sees the expression p[3], it emits code to start at the location "p," fetch the pointer value there, add three to the pointer, and finally fetch the character pointed to. In the example above, both a[3] and p[3] happen to be the character 'l', but the compiler gets there differently. (See also question 98.)

4. So what is meant by the "equivalence of pointers and arrays" in C?

A: Much of the confusion surrounding pointers in C can be traced to a misunderstanding of this statement. Saying that arrays and pointers are "equivalent" does not by any means imply that they are interchangeable.

"Equivalence" refers to the following key definition:
An lvalue of type array-of-T which appears in an expression decays (with three exceptions) into a pointer to its first element; the type of the resultant pointer is pointer-to-T.

(The exceptions are when the array is the operand of the sizeof() operator or of the & operator, or is a literal string initializer for a character array.)

As a consequence of this definition, there is not really any difference in the behavior of the "array subscripting" operator [] as it applies to arrays and pointers. In an expression of the form a[i], the array reference "a" decays into a pointer, following the rule above, and is then subscripted exactly as would be a pointer variable in the expression p[i]. In either case, the expression
x[i] (where x is an array or a pointer) is, by definition, exactly equivalent to *((x)+(i)).
References: K&R I Sec. 5.3 pp. 93-6; K&R II Sec. 5.3 p. 99; H&S Sec. 5.4.1 p. 93; ANSI Sec. 3.3.2.1, Sec. 3.3.6 .

5. Then why are array and pointer declarations interchangeable as function formal parameters?

A: Since arrays decay immediately into pointers, an array is never actually passed to a function. Therefore, any parameter declarations which "look like" arrays, e.g.
f(a)
char a[];

are treated by the compiler as if they were pointers, since that is what the function will receive if an array is passed:
f(a)
char *a;

Th1is conversion holds only within function formal parameter declarations, nowhere else. If this conversion bothers you, avoid it; many people have concluded that the confusion it causes outweighs the small advantage of having the declaration "look like" the call and/or the uses within the function.

References: K&R I Sec. 5.3 p. 95, Sec. A10.1 p. 205; K&R II Sec. 5.3 p. 100, Sec. A8.6.3 p. 218, Sec. A10.1 p. 226; H&S Sec. 5.4.3 p. 96; ANSI Sec. 3.5.4.3, Sec. 3.7.1, CT&P Sec. 3.3 pp. 33-4.

6. Someone explained to me that arrays were really just constant pointers.

A: That person did you a disservice. An array name is "constant" in that it cannot be assigned to, but an array is _not_ a pointer, as the discussion and pictures in question 16 should make clear.

7. I came across some "joke" code containing the "expression" 5["abcdef"] . How can this be legal C?

A: Yes, Virginia, array subscripting is commutative in C. This curious fact follows from the pointer definition of array subscripting, namely that a[e] is exactly equivalent to *((a)+(e)), for _any_ expression e and primary expression a, as long as one of them is a pointer expression and one is integral. This unsuspected commutativity is often mentioned in C texts as if it were something
to be proud of, but it finds no useful application outside of the Obfuscated C Contest (see question 95).

8. My compiler complained when I passed a two-dimensional array to a routine expecting a pointer to a pointer.

A: The rule by which arrays decay into pointers is not applied recursively. An array of arrays (i.e. a two-dimensional array in C) decays into a pointer to an array, not a pointer to a pointer. Pointers to arrays can be confusing, and must be treated carefully. (The confusion is heightened by the existence of incorrect compilers, including some versions of pcc and pcc-derived lint's, which improperly accept assignments of multi-dimensional arrays to multi-level pointers.) If you are passing a two-dimensional array to a function:
int array[YSIZE][XSIZE];
f(array);

the function's declaration should match:
f(int a[][XSIZE]) {...}

or
f(int (*ap)[XSIZE]) {...} /* ap is a pointer to an array */

In the first declaration, the compiler performs the usual implicit parameter rewriting of "array of array" to "pointer to array;" in the second form the pointer declaration is explicit. Since the called function does not allocate space for the array, it does not need to know the overall size, so the number of "rows," YSIZE, can be omitted. The "shape" of the array is still important, so the "column" dimension XSIZE (and, for 3- or more dimensional arrays, the intervening ones) must be included.

If a function is already declared as accepting a pointer to a pointer, it is probably incorrect to pass a two-dimensional array directly to it.

9. How do I declare a pointer to an array?

A: Usually, you don't want to. Consider using a pointer to one of the array's elements instead. Arrays of type T decay into pointers to type T, which is convenient; subscripting or incrementing the resultant pointer access the individual members of the array. True pointers to arrays, when subscripted or incremented, step over entire arrays, and are generally only useful when operating on multidimensional arrays, if at all. (See question 22 above.) When people speak casually of a pointer to an array, they usually mean a pointer to its first element.

If you really need to declare a pointer to an entire array, use something like "int (*ap)[N];" where N is the size of the array. (See also question 66.) If the size of the array is unknown, N can be omitted, but the resulting type, "pointer to array of unknown size," is useless.

10. How can I dynamically allocate a multidimensional array?

A: It is usually best to allocate an array of pointers, and then initialize each pointer to a dynamically allocated "row." The resulting "ragged" array can save space, although it is not necessarily contiguous in memory as a real array would be. Here is a two-dimensional example:
int **array = (int **)malloc(nrows * sizeof(int *));
for(i = 0; i < nrows; i++)
array[i] = (int *)malloc(ncolumns * sizeof(int));

(In "real" code, of course, malloc should be declared correctly, and each return value checked.)

You can keep the array's contents contiguous, while making later reallocation of individual rows difficult, with a bit of explicit pointer arithmetic:
int **array = (int **)malloc(nrows * sizeof(int *));
array[0] = (int *)malloc(nrows * ncolumns * sizeof(int));
for(i = 1; i < nrows; i++)
array[i] = array[0] + i * ncolumns;

In either case, the elements of the dynamic array can be accessed with normal-looking array subscripts: array[i][j].

If the double indirection implied by the above schemes is for some reason unacceptable, you can simulate a two-dimensional array with a single, dynamically allocated one-dimensional array:
int *array = (int *)malloc(nrows * ncolumns * sizeof(int));

However, you must now perform subscript calculations manually, accessing the i,jth element with array[i * ncolumns + j]. (A macro can hide the explicit calculation, but invoking it then requires parentheses and commas, which don't look exactly like multidimensional array subscripts.)

11. I have a char * pointer that happens to point to some ints, and I want to step it over them. Why doesn't
((int *)p)++;
work?

A: In C, a cast operator does not mean "pretend these bits have a different type, and treat them accordingly;" it is a conversion operator, and by definition it yields an rvalue, which cannot be assigned to, or incremented with ++. (It was an anomaly in certain versions of pcc that expressions such as the above were ever accepted.) Say what you mean: use
p = (char *)((int *)p + 1);

ANSI C Questions

1. What is the "ANSI C Standard?"

A: In 1983, the American National Standards Institute commissioned a committee, X3J11, to standardize the C language. After a long, arduous process, including several widespread public reviews, the committee's work was finally ratified as an American National Standard, X3.159-1989, on December 14, 1989, and published in the spring of 1990. For the most part, ANSI C standardizes existing practice, with a few additions from C++ (most notably function prototypes) and support for multinational character sets (including the much-lambasted trigraph sequences). The ANSI C standard also formalizes the C run-time library support routines.

The published Standard includes a "Rationale," which explains many of its decisions, and discusses a number of subtle points, including several of those covered here. (The Rationale is "not part of ANSI Standard X3.159-1989, but is included for information only.")

The Standard has been adopted as an international standard, ISO/IEC 9899:1990, although the Rationale is currently not included.

2. How can I get a copy of the Standard?

A: Copies are available from
American National Standards Institute
1430 Broadway
New York, NY 10018 USA
(+1) 212 642 4900
or
Global Engineering Documents
2805 McGaw Avenue
Irvine, CA 92714 USA
(+1) 714 261 1455
(800) 854 7179 (U.S. & Canada)

The cost from ANSI is $50.00, plus $6.00 shipping. Quantity discounts are available. (Note that ANSI derives revenues to support its operations from the sale of printed standards, so
electronic copies are _not_ available.)
Silicon Press, ISBN 0-929306-07-4, has printed the Rationale, by itself.

3. Does anyone have a tool for converting old-style C programs to ANSI C, or for automatically generating prototypes?

A: Two programs, protoize and unprotoize, convert back and forth between prototyped and "old style" function definitions and declarations. (These programs do _not_ handle full-blown
translation between "Classic" C and ANSI C.) These programs exist as patches to the FSF GNU C compiler, gcc. Look for the file protoize-1.39.0 in pub/gnu at prep.ai.mit.edu (18.71.0.38), or at several other FSF archive sites.

Several prototype generators exist, many as modifications to lint. (See also question 94.)

4. What's the difference between "char const *p" and "char * const p"?

A: "char const *p" is a pointer to a constant character (you can't change the character); "char * const p" is a constant pointer to a (variable) character (i.e. you can't change the pointer). (Read these "inside out" to understand them. See question 66.)

5. My ANSI compiler complains about a mismatch when it sees
extern int func(float);
int func(x)
float x;
{...

A: You have mixed the new-style prototype declaration "extern int func(float);" with the old-style definition "int func(x) float x;". Old C (and ANSI C, in the absence of prototypes) silently promotes floats to doubles when passing them as arguments, and arranges that doubles being passed are coerced back to floats if the formal parameters are declared that way.

The problem can be fixed either by using new-style syntax consistently in the definition:
int func(float x) { ... }

or by changing the new-style prototype declaration to match the old-style definition:
extern int func(double);

(In this case, it would be clearest to change the old-style definition to use double as well, as long as the address of that parameter is not taken.)

6. I'm getting strange syntax errors inside code which I've #ifdeffed out.

A: Under ANSI C, the text inside a "turned off" #if, #ifdef, or #ifndef must still consist of "valid preprocessing tokens." This means that there must be no unterminated comments or quotes (note particularly that an apostrophe within a contracted word could look like the beginning of a character constant), and no newlines inside quotes. Therefore, natural-language comments and pseudocode should always be written between the "official" comment delimiters /* and
*/. (But see also question 96.)


7. Can I declare main as void, to shut off these annoying "main returns no value" messages? (I'm calling exit(), so main doesn't return.)

A: No. main must be declared as returning an int, and as taking either zero or two arguments (of the appropriate type). If you're calling exit() but still getting warnings, you'll have to insert a redundant return statement (or use a "notreached" directive, if available).


8. Why does the ANSI Standard not guarantee more than six monocase characters of external identifier significance?

A: The problem is older linkers, which are neither under the control of the ANSI standard nor the C compiler developers on the systems, which have them. The limitation is only those identifiers be
_significant_ in the first six characters, not that they be restricted to six characters in length. This limitation is annoying, but certainly not unbearable, and is marked in the
Standard as "obsolescent," i.e. a future revision will likely relax it.

This concession to current, restrictive linkers really had to be made, no matter how vehemently some people oppose it. (The Rationale notes that its retention was "most painful.") If you disagree, or have thought of a trick by which a compiler burdened with a restrictive linker could present the C programmer with the appearance of more significance in external identifiers, read the excellently worded section 3.1.2 in the X3.159 Rationale (see question 28), which discusses several such schemes and explains why they could not be mandated.


9. What was noalias and what ever happened to it?

A: noalias was another type qualifier, in the same syntactic class as const and volatile, which was intended to assert that the object pointed to was not also pointed to ("aliased") by other pointers.
It was phenomenally difficult to define precisely and explain coherently, and sparked widespread, acrimonious debate. Because of the criticism and the difficulty of defining noalias well, the
Committee wisely declined to adopt it, in spite of its superficial attractions.


10. What are #pragmas and what are they good for?

A: The #pragma directive provides a single, well defined “escape hatch” which can be used for all sorts of implementation-specific controls and extensions: source listing control, structure packing, warning suppression (like the old lint/* NOTREACHED*/ comments), etc.

Preprocessor Questions

1. How can I write a generic macro to swap two values?

A: There is no good answer to this question. If the values are integers, a well-known trick using exclusive-OR could perhaps be used, but it will not work for floating-point values or pointers, (and it will not work if the two values are the same variable, and the "obvious" supercompressed implementation for integral types a^=b^=a^=b is, strictly speaking, illegal due to multiple side-
effects, and...). If the macro is intended to be used on values of arbitrary type (the usual goal), it cannot use a temporary, since it does not know what type of temporary it needs, and standard C
does not provide a typeof operator.

The best all-around solution is probably to forget about using a macro, unless you don't mind passing in the type as a third argument.

2. I have some old code that tries to construct identifiers with a macro like
#define Paste(a, b) a/**/b
but it doesn't work any more.

A: That comments disappeared entirely and could therefore be used for token pasting was an undocumented feature of some early preprocessor implementations, notably Reiser's. ANSI affirms (as did K&R) that comments are replaced with white space. However, since the need for pasting tokens was demonstrated and real, ANSI introduced a well-defined token-pasting operator, ##, which can be used like this:
#define Paste(a, b) a##b


3. What's the best way to write a multi-statement cpp macro?

A: The usual goal is to write a macro that can be invoked as if it were a single function-call statement. This means that the "caller" will be supplying the final semicolon, so the macro body should not. The macro body cannot be a simple brace-delineated compound statement, because syntax errors would result if it were invoked (apparently as a single statement, but with a resultant extra semicolon) as the if branch of an if/else statement with an explicit else clause.

The traditional solution is to use
#define Func() do { \
/* declarations */ \
stmt1; \
stmt2; \
/* ... */ \
} while(0) /* (no trailing ; ) */

When the "caller" appends a semicolon, this expansion becomes a single statement regardless of context. (An optimizing compiler will remove any "dead" tests or branches on the constant condition 0, although lint may complain.)

If all of the statements in the intended macro are simple expressions, with no declarations or loops, another technique is to write a single, parenthesized expression using one or more comma operators. (This technique also allows a value to be "returned.")

4. How can I write a cpp macro which takes a variable number of arguments?

A: One popular trick is to define the macro with a single argument, and call it with a double set of parentheses, which appear to the preprocessor to indicate a single argument:
#define DEBUG(args) {printf("DEBUG: "); printf args;}
if(n != 0) DEBUG(("n is %d\n", n));

The obvious disadvantage is that the caller must always remember to use the extra parentheses. (It is often best to use a bona-fide function, which can take a variable number of arguments in a well-defined way, rather than a macro.

Memory Allocation Questions

1. Why doesn't this fragment work?
char *answer;
printf("Type something:\n");
gets(answer);
printf("You typed \"%s\"\n", answer);

A: The pointer variable "answer," which is handed to the gets function as the location into which the response should be stored, has not been set to point to any valid storage. That is, we cannot say where the pointer "answer" points. (Since local variables are not initialized, and typically contain garbage, it is not even guaranteed that "answer" starts out as a null pointer.

The simplest way to correct the question-asking program is to use a local array, instead of a pointer, and let the compiler worry about allocation:

#include
char answer[100], *p;
printf("Type something:\n");
fgets(answer, 100, stdin);
if((p = strchr(answer, '\n')) != NULL)
*p = '\0';
printf("You typed \"%s\"\n", answer);

Note that this example also uses fgets instead of gets (always a good idea), so that the size of the array can be specified, so that fgets will not overwrite the end of the array if the user types an overly long line. (Unfortunately for this example, fgets does not automatically delete the trailing \n, as gets would.) It would also be possible to use malloc to allocate the answer buffer, and/or to parameterize its size (#define ANSWERSIZE 100).

2. I can't get strcat to work. I tried
char *s1 = "Hello, ";
char *s2 = "world!";
char *s3 = strcat(s1, s2);

but I got strange results.

A: Again, the problem is that space for the concatenated result is not properly allocated. C does not provide an automatically-managed string type. C compilers only allocate memory for objects explicitly mentioned in the source code (in the case of "strings," this includes character arrays and string literals). The programmer must arrange (explicitly) for sufficient space for the
results of run-time operations such as string concatenation, typically by declaring arrays, or by calling malloc.

strcat performs no allocation; the second string is appended to the first one, in place. Therefore, one fix would be to declare the first string as an array with sufficient space:

char s1[20] = "Hello, ";

Since strcat returns the value of its first argument (s1, in this case), the s3 variable is superfluous.


3. But the man page for strcat says that it takes two char *'s as arguments. How am I supposed to know to allocate things?

A: In general, when using pointers you _always_ have to consider memory allocation, at least to make sure that the compiler is doing it for you. If a library routine's documentation does not explicitly mention allocation, it is usually the caller's problem.

The Synopsis section at the top of a Unix-style man page can be misleading. The code fragments presented there are closer to the function definition used by the call's implementor than the invocation used by the caller. In particular, many routines which accept pointers (e.g. to structs or strings), are usually called with the address of some object (a struct, or an array – see questions 18 and 19.) Another common example is stat().

4. You can't use dynamically-allocated memory after you free it, can you?

A: No. Some early man pages for malloc stated that the contents of freed memory was "left undisturbed;" this ill-advised guarantee was never universal and is not required by ANSI.

Few programmers would use the contents of freed memory deliberately, but it is easy to do so accidentally. Consider the following (correct) code for freeing a singly-linked list:

struct list *listp, *nextp;
for(listp = base; listp != NULL; listp = nextp) {
nextp = listp->next;
free((char *)listp);
}

and notice what would happen if the more-obvious loop iteration expression listp = listp->next were used, without the temporary nextp pointer.


5. How does free() know how many bytes to free?

A: The malloc/free package remembers the size of each block it allocates and returns, so it is not necessary to remind it of the size when freeing.

6. Is it legal to pass a null pointer as the first argument to realloc()? Why would you want to?

A: ANSI C sanctions this usage (and the related realloc(..., 0), which frees), but several earlier implementations do not support it, so it is not widely portable. Passing an initially-null pointer to
realloc can make it easier to write a self-starting incremental allocation algorithm.


7. What is the difference between calloc and malloc? Is it safe to use calloc's zero-fill guarantee for pointer and floating-point values? Does free work on memory allocated with calloc, or do you need a cfree?

A: calloc(m, n) is essentially equivalent to

p = malloc(m * n);
memset(p, 0, m * n);

The zero fill is all-bits-zero, and does not therefore guarantee useful zero values for pointers (see questions 1-14) or floating- point values. free can (and should) be used to free the memory allocated by calloc.


8. What is alloca and why is its use discouraged?

A: alloca allocates memory which is automatically freed when the function which called alloca returns. That is, memory allocated with alloca is local to a particular function's "stack frame" or
context.

alloca cannot be written portably, and is difficult to implement on machines without a stack. Its use is problematical (and the obvious implementation on a stack-based machine fails) when its return value is passed directly to another function, as in fgets(alloca(100), 100, stdin).

For these reasons, alloca cannot be used in programs, which must be widely portable, no matter how useful it might be.

C Structures Questions

1. I heard that structures could be assigned to variables and passed to and from functions, but K&R I says not.

A: What K&R I said was that the restrictions on struct operations would be lifted in a forthcoming version of the compiler, and in fact struct assignment and passing were fully functional in
Ritchie's compilers even as K&R I was being published. Although a few early C compilers lacked struct assignment, all modern compilers support it, and it is part of the ANSI C standard, so there should be no reluctance to use it.


2. How does struct passing and returning work?

A: When structures are passed as arguments to functions, the entire struct is typically pushed on the stack, using as many words as are required. (Pointers to structures are often chosen precisely to avoid this overhead.)

Structures are typically returned from functions in a location pointed to by an extra, compiler-supplied "hidden" argument to the function. Older compilers often used a special, static location for structure returns, although this made struct-valued functions nonreentrant, which ANSI C disallows.

Reference: ANSI Sec. 2.2.3 p. 13.

3. The following program works correctly, but it dumps core after it finishes. Why?

struct list
{
char *item;
struct list *next;
}

/* Here is the main program. */

main(argc, argv)
...

A: A missing semicolon causes the compiler to believe that main return a struct list. (The connection is hard to see because of the intervening comment.) Since struct-valued functions are usually implemented by adding a hidden return pointer, the generated code for main() actually expects three arguments, although only two were passed (in this case, by the C start-up code). See also question 101.


4. Why can't you compare structs?

A: There is no reasonable way for a compiler to implement struct comparison, which is consistent with C's low-level flavor. A byte-by-byte comparison could be invalidated by random bits present in unused "holes" in the structure (such padding is used to keep the alignment of later fields correct). A field-by-field comparison would require unacceptable amounts of repetitive, in-line code for large structures.

If you want to compare two structures, you must write your own function to do so. C++ would let you arrange for the == operator to map to your function.

5. I came across some code that declared a structure like this:
struct name
{
int namelen;
char name[1];
};

and then did some tricky allocation to make the name array act like it had several elements. Is this legal and/or portable?

A: This technique is popular, although Dennis Ritchie has called it "unwarranted chumminess with the compiler." The ANSI C standard allows it only implicitly. It seems to be portable to all known implementations. (Compilers which check array bounds carefully might issue warnings.)

6. How can I determine the byte offset of a field within a structure?

A: ANSI C defines the offsetof macro, which should be used if available; see . If you don't have it, a suggested implementation is

#define offsetof(type, mem) ((size_t) \
((char *)&((type *) 0)->mem - (char *)((type *) 0)))

This implementation is not 100% portable; some compilers may legitimately refuse to accept it.

See the next question for a usage hint.


7. How can I access structure fields by name at run time?

A: Build a table of names and offsets, using the offsetof() macro. The offset of field b in struct a is

offsetb = offsetof(struct a, b)

If structp is a pointer to an instance of this structure, and b is an int field with offset as computed above, b's value can be set indirectly with

*(int *)((char *)structp + offsetb) = value;

Sharepoint Interview Questions-1

• what is SharePoint?
Portal Collaboration Software.
• what is the difference between SharePoint Portal Server and Windows SharePoint Services?
SharePoint Portal Server is the global portal offering features like global navigation and searching. Windows SharePoint Services is more content management based with document libraries and lists. You apply information to certain areas within your portal from Windows SharePoint Services or directly to portal areas.
• what is a document library?
A document library is where you upload your core documents. They consist of a row and column view with links to the documents. When the document is updated so is the link on your site. You can also track metadata on your documents. Metadata would consist of document properties.
• what is a meeting workspace?
A meeting workspace is a place to store information, attendees, and tasks related to a specific meeting.
• what is a document workspace?
Document workspaces consist of information surrounding a single or multiple documents.
• what is a web part?
Web parts consist of xml queries to full SharePoint lists or document libraries. You can also develop your own web parts and web part pages.
• what is the difference between a document library and a form library?
Document libraries consist of your core documents. An example would be a word document, excel, powerpoint, visio, pdf, etc… Form libraries consist of XML forms.
• what is a web part zone?
Web part zones are what your web parts reside in and help categorize your web parts when designing a page.
• how is security managed in SharePoint?
Security can be handled at the machine, domain, or sharepoint level.
• how are web parts developed?
Web parts are developed in Visual Studio .Net. VS.Net offers many web part and page templates and can also be downloaded from the Microsoft site.
• what is a site definition?
It’s a methods for providing prepackaged site and list content.
• what is a template?
A template is a pre-defined set of functions or settings that can be used over time. There are many templates within SharePoint, Site Templates, Document Templates, Document Library and List Templates.
• how do you install web parts?
Web Parts should be distributed as a .CAB (cabinet) file using the MSI Installer.
• what is CAML?
stands for Collaborative Application Markup Language and is an XML-based language that is used in Microsoft Windows SharePoint Services to define sites and lists, including, for example, fields, views, or forms, but CAML is also used to define tables in the Windows SharePoint Services database during site provisioning.
• what is a DWP?
the file extension of a web part.
• what is the GAC?
Global Assembly Cache folder on the server hosting SharePoint. You place your assemblies there for web parts and services.
• what are the differences between web part page gallery, site gallery, virtual server gallery and online gallery?
Web Part Page Gallery is the default gallery that comes installed with SharePoint. Site Gallery is specific to one site. Virtual Server gallery is specific to that virtual server and online gallery are downloadable web parts from Microsoft.
• what is the difference between a site and a web?
The pages in a Web site generally cover one or more topics and are interconnected through hyperlinks. Most Web sites have a home page as their starting point. While a Web is simply a blank site with SharePoint functionality built in; meaning you have to create the site from the ground up.
• What is Microsoft Windows SharePoint Services? How is it related to Microsoft Office SharePoint Server 2007?
Windows SharePoint Services is the solution that enables you to create Web sites for information sharing and document collaboration. Windows SharePoint Services — a key piece of the information worker infrastructure delivered in Microsoft Windows Server 2003 — provides additional functionality to the Microsoft Office system and other desktop applications, and it serves as a platform for application development.
Office SharePoint Server 2007 builds on top of Windows SharePoint Services 3.0 to provide additional capabilities including collaboration, portal, search, enterprise content management, business process and forms, and business intelligence.
• What is Microsoft SharePoint Portal Server?
SharePoint Portal Server is a portal server that connects people, teams, and knowledge across business processes. SharePoint Portal Server integrates information from various systems into one secure solution through single sign-on and enterprise application integration capabilities. It provides flexible deployment and management tools, and facilitates end-to-end collaboration through data aggregation, organization, and searching. SharePoint Portal Server also enables users to quickly find relevant information through customization and personalization of portal content and layout as well as through audience targeting.
• What is Microsoft Windows Services?
Microsoft Windows Services is the engine that allows administrators to create Web sites for information sharing and document collaboration. Windows SharePoint Services provides additional functionality to the Microsoft Office System and other desktop applications, as well as serving as a plat form for application development. SharePoint sites provide communities for team collaboration, enabling users to work together on documents, tasks, and projects. The environment for easy and flexible deployment, administration, and application development.
• What is the relationship between Microsoft SharePoint Portal Server and Microsoft Windows Services?
Microsoft SharePoint Products and Technologies (including SharePoint Portal Server and Windows SharePoint Services) deliver highly scalable collaboration solutions with flexible deployment and management tools. Windows SharePoint Services provides sites for team collaboration, while Share Point Portal Server connects these sites, people, and business processes—facilitating knowledge sharing and smart organizations. SharePoint Portal Server also extends the capabilities of Windows SharePoint Services by providing organizational and management tools for SharePoint sites, and by enabling teams to publish information to the entire organization.
• Who is Office SharePoint Server 2007 designed for?
Office SharePoint Server 2007 can be used by information workers, IT administrators, and application developers.
is designed
• What are the main benefits of Office SharePoint Server 2007?

Office SharePoint Server 2007 provides a single integrated platform to manage intranet, extranet, and Internet applications across the enterprise.
* Business users gain greater control over the storage, security, distribution, and management of their electronic content, with tools that are easy to use and tightly integrated into familiar, everyday applications.
* Organizations can accelerate shared business processes with customers and partners across organizational boundaries using InfoPath Forms Services–driven solutions.
* Information workers can find information and people efficiently and easily through the facilitated information-sharing functionality and simplified content publishing. In addition, access to back-end data is achieved easily through a browser, and views into this data can be personalized.
* Administrators have powerful tools at their fingertips that ease deployment, management, and system administration, so they can spend more time on strategic tasks.
* Developers have a rich platform to build a new class of applications, called Office Business Applications, that combine powerful developer functionality with the flexibility and ease of deployment of Office SharePoint Server 2007. Through the use of out-of-the-box application services, developers can build richer applications with less code.

JAVA Interview FAQs

1. How could Java classes direct program messages to the system console, but error messages, say to a file?
2. A:The class System has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This how the standard output could be re-directed:
i. Stream st = new Stream(new FileOutputStream("output.txt")); System.setErr(st); System.setOut(st);
3. What's the difference between an interface and an abstract class?
A. An abstract class may contain code in method bodies, which is not allowed in an interface. With abstract classes, you have to inherit your class from it and Java does not allow multiple inheritance. On the other hand, you can implement multiple interfaces in your class.
4. Why would you use a synchronized block vs. synchronized method?
A. Synchronized blocks place locks for shorter periods than synchronized methods.
5. Explain the usage of the keyword transient?
A. This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers).
6. How can you force garbage collection?
A. You can't force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately.
7. How do you know if an explicit object casting is needed?
A. If you assign a superclass object to a variable of a subclass's data type, you need to do explicit casting. For example:
8. Object a; Customer b; b = (Customer) a;
i. When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.
9. What's the difference between the methods sleep() and wait()
a. A: The code sleep(1000); puts thread aside for exactly one second. The code wait(1000), causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.
10. Can you write a Java class that could be used both as an applet as well as an application?
A. Yes. Add a main() method to the applet.
11. What's the difference between constructors and other methods?
A. Constructors must have the same name as the class and can not return a value. They are only called once while regular methods could be called many times.
12. Can you call one constructor from another if a class has multiple constructors
a. A: Yes. Use this() syntax.
13. Explain the usage of Java packages.
A. This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.
14. If a class is located in a package, what do you need to change in the OS environment to be able to use it?
A. You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Let's say a class Employee belongs to a package com.xyz.hr; and is located in the file c:\dev\com\xyz\hr\Employee.java. In this case, you'd need to add c:\dev to the variable CLASSPATH. If this class contains the method main(), you could test it from a command prompt window as follows:
15. c:\>java com.xyz.hr.Employee
16. What's the difference between J2SDK 1.5 and J2SDK 5.0?
A. There’s no difference, Sun Microsystems just re-branded this version.
17. What would you use to compare two String variables - the operator == or the method equals()?
A. I'd use the method equals() to compare the values of the Strings and the == to check if two variables point at the same instance of a String object.
18. Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?
A. Yes, it does. The FileNoFoundException is inherited from the IOException. Exception's subclasses have to be caught first.
19. Can an inner class declared inside of a method access local variables of this method?
A. It's possible if these variables are final.
20. What can go wrong if you replace && with & in the following code:
a. String a=null; if (a!=null && a.length()>10) {...}
b. A:A single ampersand here would lead to a NullPointerException.
21. What's the main difference between a Vector and an ArrayList
A. Java Vector class is internally synchronized and ArrayList is not.
22. When should the method invokeLater()be used?
A. This method is used to ensure that Swing components are updated through the event-dispatching thread.
23. How can a subclass call a method or a constructor defined in a superclass?
A. Use the following syntax: super.myMethod(); To call a constructor of the superclass, just write super(); in the first line of the subclass's constructor.
24. What's the difference between a queue and a stack?
A. Stacks works by last-in-first-out rule (LIFO), while queues use the FIFO rule
25. You can create an abstract class that contains only abstract methods. On the other hand, you can create an interface that declares the same methods. So can you use abstract classes instead of interfaces?
A. Sometimes. But your class may be a descendent of another class and in this case the interface is your only option.

26. What comes to mind when you hear about a young generation in Java?
A. Garbage collection.
27. What comes to mind when someone mentions a shallow copy in Java?
A. Object cloning.
28. If you're overriding the method equals() of an object, which other method you might also consider?
A. hashCode()
29. You are planning to do an indexed search in a list of objects. Which of the two Java collections should you use:
ArrayList or LinkedList?
A. ArrayList
30. How would you make a copy of an entire Java object with its state?
A. Have this class implement Cloneable interface and call its method clone().
31. How can you minimize the need of garbage collection and make the memory use more effective?
A. Use object pooling and weak object references.
32. There are two classes: A and B. The class B need to inform a class A when some important event has happened. What Java technique would you use to implement it?
A. If these classes are threads I'd consider notify() or notifyAll(). For regular classes you can use the Observer interface.
33. What access level do you need to specify in the class declaration to ensure that only classes from the same directory can access it?
A. You do not need to specify any access level, and Java will use a default package access level.
34. What is transient variable?
A: Transient variable can't be serialize. For example if a variable is declared as transient in a Serializable class and the class is written to an ObjectStream, the value of the variable can't be written to the stream instead when the class is retrieved from the ObjectStream the value of the variable becomes null.
35. Name the containers which use Border Layout as their default layout?
A: Containers which uses Border Layout as their default are: window, Frame and Dialog classes.
36. What do you understand by Synchronization?
A: Synchronization is a process of controlling the access of shared resources by the multiple threads in such a manner that only one thread can access one resource at a time. In non synchronized multithreaded application, it is possible for one thread to modify a shared object while another thread is in the process of using or updating the object's value. Synchronization prevents such type of data corruption.
E.g. Synchronizing a function:
public synchronized void Method1 () {
// Appropriate method-related code.
}
E.g. Synchronizing a block of code inside a function:
public myFunction (){
synchronized (this) {
// Synchronized code here.
}
}
37. What is Collection API?
A:The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables if effectively replaces.
Example of classes: HashSet, HashMap, ArrayList, LinkedList, TreeSet and TreeMap.
Example of interfaces: Collection, Set, List and Map.
38. Is Iterator a Class or Interface? What is its use?
A: Iterator is an interface which is used to step through the elements of a Collection.
39. What is similarities/difference between an Abstract class and Interface? A: Differences are as follows: Interfaces provide a form of multiple inheritance. A class can extend only one other class. Interfaces are limited to public methods and constants with no implementation. Abstract classes can have a partial implementation, protected parts, static methods, etc.A Class may implement several interfaces. But in case of abstract class, a class may extend only one abstract class.Interfaces are slow as it requires extra indirection to to find corresponding method in in the actual class. Abstract classes are fast. Similarities: Neither Abstract classes or Interface can be instantiated.
40. How to define an Abstract class?
A: A class containing abstract method is called Abstract class. An Abstract class can't be instantiated.
Example of Abstract class:
abstract class testAbstractClass {
protected String myString;
public String getMyString() {
return myString;
}
public abstract string anyAbstractFunction();
}
41. How to define an Interface?
A: In Java Interface defines the methods but does not implement them. Interface can include constants. A class that implements the interfaces is bound to implement all the methods defined in Interface.
Emaple of Interface:

public interface sampleInterface {
public void functionOne();

public long CONSTANT_ONE = 1000;
}
42. Explain the user defined Exceptions?
A: User defined Exceptions are the separate Exception classes defined by the user for specific purposed. An user defined can created by simply sub-classing it to the Exception class. This allows custom exceptions to be generated (using throw) and caught in the same way as normal exceptions.
Example:
class myCustomException extends Exception {
// The class simply has to exist to be an exception
}
43. Explain the new Features of JDBC 2.0 Core API?
A: The JDBC 2.0 API includes the complete JDBC API, which includes both core and Optional Package API, and provides inductrial-strength database computing capabilities.
New Features in JDBC 2.0 Core API:
a. Scrollable result sets- using new methods in the ResultSet interface allows programmatically move the to particular row or to a position relative to its current position
b. JDBC 2.0 Core API provides the Batch Updates functionality to the java applications.
c. Java applications can now use the ResultSet.updateXXX methods.
d. New data types - interfaces mapping the SQL3 data types
e. Custom mapping of user-defined types (UTDs)
f. Miscellaneous features, including performance hints, the use of character streams, full precision for java.math.BigDecimal values, additional security, and support for time zones in date, time, and timestamp values.
44. Explain garbage collection?
A: Garbage collection is one of the most important feature of Java. Garbage collection is also called automatic memory management as JVM automatically removes the unused variables/objects (value is null) from the memory. User program cann't directly free the object from memory, instead it is the job of the garbage collector to automatically free the objects that are no longer referenced by a program. Every class inherits finalize() method from java.lang.Object, the finalize() method is called by garbage collector when it determines no more references to the object exists. In Java, it is good idea to explicitly assign null into a variable when no more in use. I Java on calling System.gc() and Runtime.gc(), JVM tries to recycle the unused objects, but there is no guarantee when all the objects will garbage collected.
45. How you can force the garbage collection?
A: Garbage collection automatic process and can't be forced.
46. What is OOPS?
A: OOP is the common abbreviation for Object-Oriented Programming.
47. Describe the principles of OOPS.
A: There are three main principals of oops which are called Polymorphism, Inheritance and Encapsulation.
48. Explain the Encapsulation principle.
A: Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse. One way to think about encapsulation is as a protective wrapper that prevents code and data from being arbitrarily accessed by other code defined outside the wrapper.
49. Explain the Inheritance principle.
A: Inheritance is the process by which one object acquires the properties of another object.
50. Explain the Polymorphism principle.
A: The meaning of Polymorphism is something like one name many forms. Polymorphism enables one entity to be used as as general category for different types of actions. The specific action is determined by the exact nature of the situation. The concept of polymorphism can be explained as "one interface, multiple methods".
51. Explain the different forms of Polymorphism.
A: From a practical programming viewpoint, polymorphism exists in three distinct forms in Java:
Method overloading
Method overriding through inheritance
Method overriding through the Java interface.
52. What are Access Specifiers available in Java?
A: Access specifiers are keyword that determines the type of access to the member of a class. These are:
Public
Protected
Private
Defaults
53. Describe the wrapper classes in Java.
A: Wrapper class is wrapper around a primitive data type. An instance of a wrapper class contains, or wraps, a primitive value of the corresponding type.
a. Primitive b. Wrapper
c. boolean d. java.lang.Boolean
e. byte f. java.lang.Byte
g. char h. java.lang.Character
i. double j. java.lang.Double
k. float l. java.lang.Float
m. int n. java.lang.Integer
o. long p. java.lang.Long
q. short r. java.lang.Short
s. void t. java.lang.Void


54. Read the
55. following program:
a. A:public class test {
public static void main(String [] args) {
int x = 3;
int y = 1;
if (x = y)
System.out.println("Not equal");
else
System.out.println("Equal");
}
}
56. What is the result?
A. The output is “Equal”
B. The output in “Not Equal”
C. An error at " if (x = y)" causes compilation to fall.
D. The program executes but no output is show on console.
Answer: C
57. Can there be an abstract class with no abstract methods in it? - Yes
58. Can an Interface be final? - No
59. Can an Interface have an inner class? - Yes.
a. public interface abc
b. {
c. static int i=0; void dd();
d. class a1
e. {
f. a1()
g. {
h. int j;
i. System.out.println("inside");
j. };
k. public static void main(String a1[])
l. {
m. System.out.println("in interfia");
n. }
o. }
p. }
60. Can we define private and protected modifiers for variables in interfaces? - No
61. What is Externalizable? - Externalizable is an Interface that extends Serializable Interface. And sends data into Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput out) and readExternal(ObjectInput in)
62. What modifiers are allowed for methods in an Interface? - Only public and abstract modifiers are allowed for methods in interfaces.
63. What is a local, member and a class variable? - Variables declared within a method are “local” variables. Variables declared within the class i.e not within any methods are “member” variables (global variables). Variables declared within the class i.e not within any methods and are defined as “static” are class variables
64. What are the different identifier states of a Thread? – The different identifiers of a Thread are: R - Running or runnable thread, S - Suspended thread, CW - Thread waiting on a condition variable, MW - Thread waiting on a monitor lock, MS - Thread suspended waiting on a monitor lock
65. What are some alternatives to inheritance? - Delegation is an alternative to inheritance. Delegation means that you include an instance of another class as an instance variable, and forward messages to the instance. It is often safer than inheritance because it forces you to think about each message you forward, because the instance is of a known class, rather than a new class, and because it doesn’t force you to accept all the methods of the super class: you can provide only the methods that really make sense. On the other hand, it makes you write more code, and it is harder to re-use (because it is not a subclass).
66. Why isn’t there operator overloading? - Because C++ has proven by example that operator overloading makes code almost impossible to maintain. In fact there very nearly wasn’t even method overloading in Java, but it was thought that this was too useful for some very basic methods like print(). Note that some of the classes like DataOutputStream have unoverloaded methods like writeInt() and writeByte().
67. What does it mean that a method or field is “static”? - Static variables and methods are instantiated only once per class. In other words they are class variables, not instance variables. If you change the value of a static variable in a particular object, the value of that variable changes for all instances of that class. Static methods can be referenced with the name of the class rather than the name of a particular object of the class (though that works too). That’s how library methods like System.out.println() work. out is a static field in the java.lang.System class.
68. How do I convert a numeric IP address like 192.18.97.39 into a hostname like java.sun.com?
String hostname = InetAddress.getByName("192.18.97.39").getHostName();
69. Why do threads block on I/O? - Threads block on i/o (that is enters the waiting state) so that other threads may execute while the I/O operation is performed.
70. What is synchronization and why is it important? - With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object’s value. This often leads to significant errors.
71. Is null a keyword? - The null value is not a keyword.
72. Which characters may be used as the second character of an identifier, but not as the first character of an identifier? - The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.
73. What modifiers may be used with an inner class that is a member of an outer class? - A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.
74. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters? - Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.
75. What are wrapped classes? - Wrapped classes are classes that allow primitive types to be accessed as objects.
76. What restrictions are placed on the location of a package statement within a source code file? - A package statement must appear as the first line in a source code file (excluding blank lines and comments).
77. What is the difference between preemptive scheduling and time slicing? - Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
78. What is a native method? - A native method is a method that is implemented in a language other than Java.
79. What are order of precedence and associativity, and how are they used? - Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left
80. What is the catch or declare rule for method declarations? - If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.
81. Can an anonymous class be declared as implementing an interface and extending a class? - An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.
82. What is the range of the char type? - The range of the char type is 0 to 2^16 - 1.
83. what is a transient variable?A transient variable is a variable that may not be serialized.
84. Which containers use a border Layout as their default layout?The window, Frame and Dialog classes use a border layout as their default layout.
85. Why do threads block on I/O?Threads block on i/o (that is enters the waiting state) so that other threads may execute while the i/o Operation is performed.
86. How are Observer and Observable used?Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
87. What is synchronization and why is it important? With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.
88. Can a lock be acquired on a class? Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.
89. What's new with the stop(), suspend() and resume() methods in JDK 1.2?The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.
90. Is null a keyword? The null value is not a keyword.
91. What is the preferred size of a component? The preferred size of a component is the minimum component size that will allow the component to display normally.
92. What method is used to specify a container's layout? The setLayout() method is used to specify a container's layout.
93. Which containers use a FlowLayout as their default layout?The Panel and Applet classes use the FlowLayout as their default layout.
94. What state does a thread enter when it terminates its processing? When a thread terminates its processing, it enters the dead state.
95. What is the Collections API? The Collections API is a set of classes and interfaces that support operations on collections of objects.
96. Which characters may be used as the second character of an identifier, but not as the first character of an identifier? The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.
97. What is the List interface? The List interface provides support for ordered collections of objects.
98. How does Java handle integer overflows and underflows? It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
99. What is the Vector class? The Vector class provides the capability to implement a growable array of objects
100. What modifiers may be used with an inner class that is a member of an outer class? A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.
101. What is an Iterator interface? The Iterator interface is used to step through the elements of a Collection.
102. What is the difference between the >> and >>> operators? The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.
103. Which method of the Component class is used to set the position and size of a component? setBounds()
104. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters? Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.
105. What is the difference between yielding and sleeping? When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.
106. Which java.util classes and interfaces support event handling? The EventObject class and the EventListener interface support event processing.
107. Is sizeof a keyword? The sizeof operator is not a keyword.
108. What are wrapped classes? Wrapper classes are classes that allow primitive types to be accessed as objects.
109. Does garbage collection guarantee that a program will not run out of memory? Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection
110. What restrictions are placed on the location of a package statement within a source code file? A package statement must appear as the first line in a source code file (excluding blank lines and comments).
111. Can an object's finalize() method be invoked while it is reachable? An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects.
112. What is the immediate superclass of the Applet class? Panel
113. What is the difference between preemptive scheduling and time slicing? Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
114. Name three Component subclasses that support painting. The Canvas, Frame, Panel, and Applet classes support painting.
115. What value does readLine() return when it has reached the end of a file? The readLine() method returns null when it has reached the end of a file.
116. What is the immediate superclass of the Dialog class? Window
117. What is clipping? Clipping is the process of confining paint operations to a limited area or shape.
118. What is a native method? A native method is a method that is implemented in a language other than Java.
119. Can a for statement loop indefinitely? Yes, a for statement can loop indefinitely. For example, consider the following: for(;;);
120. What are order of precedence and associativity, and how are they used? Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left
121. When a thread blocks on I/O, what state does it enter?A thread enters the waiting state when it blocks on I/O.
122. To what value is a variable of the String type automatically initialized? The default value of an String type is null.
123. What is the catch or declare rule for method declarations? If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.
124. What is the difference between a MenuItem and a CheckboxMenuItem? The CheckboxMenuItem class extends the MenuItem class to support a menu item that may be checked or unchecked.
125. What is a task's priority and how is it used in scheduling? A task's priority is an integer value that identifies the relative order in which it should be executed with respect to other tasks. The scheduler attempts to schedule higher priority tasks before lower priority tasks.
126. What class is the top of the AWT event hierarchy? The java.awt.AWTEvent class is the highest-level class in the AWT event-class hierarchy.
127. When a thread is created and started, what is its initial state? A thread is in the ready state after it has been created and started.
128. Can an anonymous class be declared as implementing an interface and extending a class? An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.
129. What is the range of the short type? The range of the short type is -(2^15) to 2^15 - 1.
130. What is the range of the char type? The range of the char type is 0 to 2^16 - 1.
131. In which package are most of the AWT events that support the event-delegation model defined? Most of the AWT-related events of the event-delegation model are defined in the java.awt.event package. The AWTEvent class is defined in the java.awt package.
132. What is the immediate superclass of Menu? MenuItem
133. What is the purpose of finalization? The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.
134. Which class is the immediate superclass of the MenuComponent class? Object
135. What invokes a thread's run() method? After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.
136. What is the difference between the Boolean & operator and the && operator? If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.
137. Name three subclasses of the Component class. Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent
138. What is the GregorianCalendar class? The GregorianCalendar provides support for traditional Western calendars.
139. Which Container method is used to cause a container to be laid out and redisplayed? validate()
140. What is the purpose of the Runtime class? The purpose of the Runtime class is to provide access to the Java runtime system.
141. How many times may an object's finalize() method be invoked by the garbage collector? An object's finalize() method may only be invoked once by the garbage collector.
142. What is the purpose of the finally clause of a try-catch-finally statement? The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.
143. What is the argument type of a program's main() method? A program's main() method takes an argument of the String[] type.
144. Which Java operator is right associative? The = operator is right associative.
145. What is the Locale class? The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.
146. Can a double value be cast to a byte? Yes, a double value can be cast to a byte.
147. What is the difference between a break statement and a continue statement? A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.
148. What must a class do to implement an interface? It must provide all of the methods in the interface and identify the interface in its implements clause.
149. What method is invoked to cause an object to begin executing as a separate thread? The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread.
150. Name two subclasses of the TextComponent class. TextField and TextArea
151. What is the advantage of the event-delegation model over the earlier event-inheritance model? The event-delegation model has two advantages over the event-inheritance model. First, it enables event handling to be handled by objects other than the ones that generate the events (or their containers). This allows a clean separation between a component's design and its use. The other advantage of the event-delegation model is that it performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to repeatedly process unhandled events, as is the case of the event-inheritance model.
152. Which containers may have a MenuBar? Frame
153. How are commas used in the intialization and iteration parts of a for statement? Commas are used to separate multiple statements within the initialization and iteration parts of a for statement.
154. What is the purpose of the wait(), notify(), and notifyAll() methods? The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to wait for a shared resource. When a thread executes an object's wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object's notify() or notifyAll() methods.
155. What is an abstract method? An abstract method is a method whose implementation is deferred to a subclass.
156. How are Java source code files named? A Java source code file takes the name of a public class or interface that is defined within the file. A source code file may contain at most one public class or interface. If a public class or interface is defined within a source code file, then the source code file must take the name of the public class or interface. If no public class or interface is defined within a source code file, then the file must take on a name that is different than its classes and interfaces. Source code files use the .java extension.
157. What is the relationship between the Canvas class and the Graphics class? A Canvas object provides access to a Graphics object via its paint() method.
158. What are the high-level thread states? The high-level thread states are ready, running, waiting, and dead.
159. What value does read() return when it has reached the end of a file? The read() method returns -1 when it has reached the end of a file.
160. Can a Byte object be cast to a double value? No, an object cannot be cast to a primitive value.
161. What is the difference between a static and a non-static inner class? A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.
162. What is the difference between the String and StringBuffer classes? String objects are constants. StringBuffer objects are not.
163. If a variable is declared as private, where may the variable be accessed? A private variable may only be accessed within the class in which it is declared.
164. What is an object's lock and which object's have locks? An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.
165. What is the Dictionary class? The Dictionary class provides the capability to store key-value pairs.
166. How are the elements of a BorderLayout organized? The elements of a BorderLayout are organized at the borders (North, South, East, and West) and the center of a container.
167. What is the % operator? It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.
168. When can an object reference be cast to an interface reference? An object reference be cast to an interface reference when the object implements the referenced interface.
169. What is the difference between a Window and a Frame? The Frame class extends Window to define a main application window that can have a menu bar.
170. Which class is extended by all other classes? The Object class is extended by all other classes.
171. Can an object be garbage collected while it is still reachable? A reachable object cannot be garbage collected. Only unreachable objects may be garbage collected..
172. Is the ternary operator written x : y ? z or x ? y : z ? It is written x ? y : z.
173. What is the difference between the Font and FontMetrics classes? The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object.
174. How is rounding performed under integer division? The fractional part of the result is truncated. This is known as rounding toward zero.
175. What happens when a thread cannot acquire a lock on an object? If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.
176. What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy? The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.
177. What classes of exceptions may be caught by a catch clause? A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.
178. If a class is declared without any access modifiers, where may the class be accessed? A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.
179. What is the SimpleTimeZone class? The SimpleTimeZone class provides support for a Gregorian calendar.
180. What is the Map interface? The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
181. Does a class inherit the constructors of its superclass? A class does not inherit constructors from any of its superclasses.
182. For which statements does it make sense to use a label? The only statements for which it makes sense to use a label are those statements that can enclose a break or continue statement.
183. What is the purpose of the System class? The purpose of the System class is to provide access to system resources.
184. Which TextComponent method is used to set a TextComponent to the read-only state? setEditable()
185. How are the elements of a CardLayout organized? The elements of a CardLayout are stacked, one on top of the other, like a deck of cards.
186. Is &&= a valid Java operator? No, it is not.
187. Name the eight primitive Java types. The eight primitive types are byte, char, short, int, long, float, double, and boolean.
188. Which class should you use to obtain design information about an object? The Class class is used to obtain information about an object's design.
189. What is the relationship between clipping and repainting? When a window is repainted by the AWT painting thread, it sets the clipping regions to the area of the window that requires repainting.
190. Is "abc" a primitive value? The String literal "abc" is not a primitive value. It is a String object.
191. What is the relationship between an event-listener interface and an event-adapter class? An event-listener interface defines the methods that must be implemented by an event handler for a particular kind of event. An event adapter provides a default implementation of an event-listener interface.
192. What restrictions are placed on the values of each case of a switch statement? During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value.
193. What modifiers may be used with an interface declaration? An interface may be declared as public or abstract.
194. Is a class a subclass of itself? A class is a subclass of itself.
195. What is the highest-level event class of the event-delegation model? The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.
196. What event results from the clicking of a button? The ActionEvent event is generated as the result of the clicking of a button.
197. How can a GUI component handle its own events? A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener.
198. What is the difference between a while statement and a do statement? A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once.
199. How are the elements of a GridBagLayout organized? The elements of a GridBagLayout are organized according to a grid. However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.
200. What advantage do Java's layout managers provide over traditional windowing systems? Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accomodate platform-specific differences among windowing systems.
201. What is the Collection interface? The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.
202. What modifiers can be used with a local inner class? A local inner class may be final or abstract.
203. What is the difference between static and non-static variables? A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.
204. What is the difference between the paint() and repaint() methods? The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.
205. What is the purpose of the File class? The File class is used to create objects that provide access to the files and directories of a local file system.
206. Can an exception be rethrown? Yes, an exception can be rethrown.
207. Which Math method is used to calculate the absolute value of a number? The abs() method is used to calculate absolute values.
208. How does multithreading take place on a computer with a single CPU? The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
209. When does the compiler supply a default constructor for a class? The compiler supplies a default constructor for a class if no other constructors are provided.
210. When is the finally clause of a try-catch-finally statement executed? The finally clause of the try-catch-finally statement is always executed unless the thread of execution terminates or an exception occurs within the execution of the finally clause.
211. Which class is the immediate superclass of the Container class? Component
212. If a method is declared as protected, where may the method be accessed? A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.
213. How can the Checkbox class be used to create a radio button? By associating Checkbox objects with a CheckboxGroup.
214. Which non-Unicode letter characters may be used as the first character of an identifier? The non-Unicode letter characters $ and _ may appear as the first character of an identifier
215. What restrictions are placed on method overloading? Two methods may not have the same name and argument list but different return types.
216. What happens when you invoke a thread's interrupt method while it is sleeping or waiting? When a task's interrupt() method is executed, the task enters the ready state. The next time the task enters the running state, an InterruptedException is thrown.
217. What is casting? There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
218. What is the return type of a program's main() method? A program's main() method has a void return type.
219. Name four Container classes. Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane
220. What is the difference between a Choice and a List? A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices. Only one item may be selected from a Choice. A List may be displayed in such a way that several List items are visible. A List supports the selection of one or more List items.
221. What class of exceptions are generated by the Java run-time system? The Java runtime system generates RuntimeException and Error exceptions.
222. What class allows you to read objects directly from a stream? The ObjectInputStream class supports the reading of objects from input streams.
223. What is the difference between a field variable and a local variable? A field variable is a variable that is declared as a member of a class. A local variable is a variable that is declared local to a method.
224. Under what conditions is an object's finalize() method invoked by the garbage collector? The garbage collector invokes an object's finalize() method when it detects that the object has become unreachable.
225. How are this() and super() used with constructors? this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.
226. What is the relationship between a method's throws clause and the exceptions that can be thrown during the method's execution? A method's throws clause must declare any checked exceptions that are not caught within the body of the method.
227. What is the difference between the JDK 1.02 event model and the event-delegation model introduced with JDK 1.1? The JDK 1.02 event model uses an event inheritance or bubbling approach. In this model, components are required to handle their own events. If they do not handle a particular event, the event is inherited by (or bubbled up to) the component's container. The container then either handles the event or it is bubbled up to its container and so on, until the highest-level container has been tried.
228. In the event-delegation model, specific objects are designated as event handlers for GUI components. These objects implement event-listener interfaces. The event-delegation model is more efficient than the event-inheritance model because it eliminates the processing required to support the bubbling of unhandled events.
229. How is it possible for two String objects with identical values not to be equal under the == operator? The == operator compares two objects to determine if they are the same object in memory. It is possible for two String objects to have the same value, but located indifferent areas of memory.
230. Why are the methods of the Math class static? So they can be invoked as if they are a mathematical code library.
231. What Checkbox method allows you to tell if a Checkbox is checked? getState()
232. What state is a thread in when it is executing? An executing thread is in the running state.
233. What are the legal operands of the instanceof operator? The left operand is an object reference or null value and the right operand is a class, interface, or array type.
234. How are the elements of a GridLayout organized? The elements of a GridBad layout are of equal size and are laid out using the squares of a grid.
235. What an I/O filter? An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.
236. If an object is garbage collected, can it become reachable again? Once an object is garbage collected, it ceases to exist. It can no longer become reachable again.
237. What is the Set interface? The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
238. What classes of exceptions may be thrown by a throw statement? A throw statement may throw any expression that may be assigned to the Throwable type.
239. What are E and PI? E is the base of the natural logarithm and PI is mathematical value pi.
240. Are true and false keywords? The values true and false are not keywords.
241. What is a void return type? A void return type indicates that a method does not return a value.
242. What is the purpose of the enableEvents() method? The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
243. What is the difference between the File and RandomAccessFile classes? The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.
244. What happens when you add a double value to a String? The result is a String object.
245. What is your platform's default character encoding? If you are running Java on English Windows platforms, it is probably Cp1252. If you are running Java on English Solaris platforms, it is most likely 8859_1..
246. Which package is always imported by default? The java.lang package is always imported by default.
247. What interface must an object implement before it can be written to a stream as an object? An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.
248. How are this and super used? this is used to refer to the current object instance. super is used to refer to the variables and methods of the superclass of the current object instance.
249. What is the purpose of garbage collection? The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources may be reclaimed and reused.
250. What is a compilation unit? A compilation unit is a Java source code file.
251. What interface is extended by AWT event listeners? All AWT event listeners extend the java.util.EventListener interface.
252. What restrictions are placed on method overriding? Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
253. How can a dead thread be restarted? A dead thread cannot be restarted.
254. What happens if an exception is not caught? An uncaught exception results in the uncaughtException() method of the thread's ThreadGroup being invoked, which eventually results in the termination of the program in which it is thrown.
255. What is a layout manager? A layout manager is an object that is used to organize components in a container.
256. Which arithmetic operations can result in the throwing of an ArithmeticException? Integer / and % can result in the throwing of an ArithmeticException.
257. What are three ways in which a thread can enter the waiting state? A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.
258. Can an abstract class be final? An abstract class may not be declared as final.
259. What is the ResourceBundle class? The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.
260. What happens if a try-catch-finally statement does not have a catch clause to handle an exception that is thrown within the body of the try statement? The exception propagates up to the next higher level try-catch statement (if any) or results in the program's termination.
261. What is numeric promotion? Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. In numerical promotion, byte, char, and short values are converted to int values.The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required.
262. What is the difference between a Scrollbar and a ScrollPane? A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.
263. What is the difference between a public and a non-public class? A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.
264. To what value is a variable of the boolean type automatically initialized? The default value of the boolean type is false.
265. Can try statements be nested? Try statements may be tested.
266. What is the difference between the prefix and postfix forms of the ++ operator? The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.
267. What is the purpose of a statement block? A statement block is used to organize a sequence of statements as a single statement group.
268. What is a Java package and how is it used? A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
269. What modifiers may be used with a top-level class? A top-level class may be public, abstract, or final.
270. What are the Object and Class classes used for? The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.
271. How does a try statement determine which catch clause should be used to handle an exception? When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.
272. Can an unreachable object become reachable again? An unreachable object may become reachable again. This can happen when the object's finalize() method is invoked and the object performs an operation which causes it to become accessible to reachable objects.
273. When is an object subject to garbage collection? An object is subject to garbage collection when it becomes unreachable to the program in which it is used.
274. What method must be implemented by all threads? All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface.
275. What methods are used to get and set the text label displayed by a Button object? getLabel() and setLabel()
276. Which Component subclass is used for drawing and painting? Canvas
277. What are synchronized methods and synchronized statements? Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
278. What are the two basic ways in which classes that can be run as threads may be defined? A thread class may be declared as a subclass of Thread, or it may implement the Runnable interface.
279. What are the problems faced by Java programmers who don't use layout managers? Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing and positioning that will work within the constraints imposed by each windowing system.
280. What is the difference between an if statement and a switch statement? The if statement is used to select among two alternatives. It uses a boolean expression to decide which alternative should be executed. The switch statement is used to select among multiple alternatives. It uses an int expression to determine which alternative should be executed.
281. What happens when you add a double value to a String? The result is a String object.
282. What is the List interface? The List interface provides support for ordered collections of objects.
283. Describe the three OOO principles?
Encapsulation - It is the way the code and data are confined and are in isolation from the outside environment of the system.
EXAMPLE: In a car the engine can be thought about as an encapsulated which is controlled by the starter key and the gear. The operation of the engine does not affect the functioning of other parts of car like the headlight and wiper. In JAVA basis of encapsulation is the CLASS.
Inheritance - It is the process by which one object acquires the properties of another object.
Polymorphism - It is a feature that allows one interface to be used for a general class of actions. The specific action is determined by the exact nature of the situation.
EXAMPLE: In a college cafeteria if an old music is put the students would not like it , but if the latest number of Brittney Spears is put then they would love it. If analyzed then we can see that even though the process of listening is the same i.e. for the old song the students listen it from there ears and even for the latest Brittney Spears number they listen it from there ear. But there is a difference by which the students react. This difference can be explained by the concept polymorphism.
284. What is meant by Endianness? . Endianness describes how multiple data types such as short , int and long are stored in memory.If it takes two bytes to represent a short, then to predict if the most significant or the least significant comes first.If the most significant byte is first, followed by the least significant one then the machine is said to be big endian. Machines such as the SPARC and Power PC are big-endian, while the Intel x86 series is little-endian.
285. How many types of literals are there in JAVA? There are four types of literals they are Integer literals, Floating point literals, Boolean literals and character literals.
286. A note on compiling & Executing a JAVA pgm
The name of the sourcefile is called in terms of .java
A source file is called a compilation unit. This has one or more class definitions.
The name of the class should be same as that of the file.
Once compiled the .java file creates a .class file. This is done by the compiler javac
This classfile contains the byte code version of the program.
287. A note on PUBLIC , PRIVATE , STATIC , VOID & MAIN.
All Java applications begin execution by calling main ()
When a class member is defined as public. Then that member may be accessed by code outside the class in which it is declared.
The opposite of public is private which prevents a member from being used by code defined outside of its class.
The keyword static allows main() to be called without having to instantiate a particular instance of the class. This is mandatory because main () is called by the Java interpreter before any objects are made.
CASE SENSITIVE : Main () is different from main(). It is important to know that that Main() would be compiled. But the Java interpreter would report an error if it would not find main().
288. What is meant by Garbage collection? The technique that automatically destroys the dynamically created objects is called garbage collection. When no reference to an object exists, that object is assumed to be no longer needed , and memory occupied by that object can be reclaimed.
289. What are the access modifiers? There are three types of access modifiers.
Private - Makes a method or a variable accessible only from within its own class.
Protected - Makes a method or a variable accessible only to classes in the same package or subclasses of the class.
Public - Makes a class , method or variable accessible from any other class.
290. A note on keywords for Error handling.
Catch - Declares the block of code used to handle an exception.
Finally - Block of code , usually following a typecatch statement, which is executed no matter what program flow occurs when dealing with an exception.
Throw - Used to pass an exception up to the method that calls this method.
Throws - Indicates the method will pass an exception to the method that called it.
Try - Block of code that will be tried but which may cause an exception.
Assert - Evaluates a conditional _expression to verify the programmer's assumption.
291. How many ways can you represent integer numbers in JAVA? There are three ways; you can represent integer numbers in JAVA. They are decimal (base 10) , octal (base 8) , and hexadecimal (base 16).
292. A note on defining floating point literal ? A floating point literal is defined as float g = 3576.2115F.
293. A note on arrays of object references? If the array type is CLASS then one can put objects of any subclass of the declared type into the array. The following example on sports explains the above concept :
class sports { }
class football extends sports { }
class hockey extends sports { }
class baseball extends sports { }
sports [ ] mysports = { new football (),
new hockey (),
new baseball ()};
294. What is meant by "instanceof" comparison? It is used for object reference variables only.You can use it to check whether an object is of a particular type.
295. When is a method said to be overloaded? Two or more methods are defined within the same class that shares the same name and their parameter declarations are different then the methods are said to be overloaded.
296. What is meant by Recursion? It is the process of defining something in terms of itself. In terms of JAVA it is the attribute that allows a method to call itself. The following example of calculating a factorial gives an example of recursion.
class Factorial {
int fact (int n) {
int result;
if (n= 1) return 1;
result = fact(n -1) * n;
return result;
}
}
class Recursion {
Public static void main (string args[ ]) {
Factorial f = new Factorial ();
system.out.println ("Factorial of 10 is " + f.fact(10));
}
}
297. A cool example to explain the concept of METHOD in JAVA. Let us say you are in Mcdonalds and you order for #7 for here with medium coke. The cashier takes your order and punches it on the computer. The folks in the kitchen get the order and they get the crispy chicken and pass it on to the guy who puts a medium fries and finally a medium coke is filled and the order is served to you. In other terms if all this was supposed to be done by a robot then it could have been programmed the following way.
void #7forherewithmediumcoke( )
{
Get (crispy chicken, lattice, butter, fries, coke);
make (sandwich);
fill (coke, fries);
}
298. How could a Java program redirect error messages to a file while sending other messages to the system console? The class System has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This how the standard output could be re-directed:
Stream st = new Stream(new FileOutputStream("output.txt")); System.setErr(st); System.setOut(st);
299. What's the difference between an interface and an abstract class? An abstract class may contain code in method bodies, which is not allowed in an interface. With abstract classes, you have to inherit your class from it and Java does not allow multiple inheritance. On the other hand, you can implement multiple interfaces in your class.
300. Why would you use a synchronized block vs. synchronized method? Synchronized blocks place locks for shorter periods than synchronized methods.
301. You can create an abstract class that contains only abstract methods. On the other hand, you can create an interface that declares the same methods. So can you use abstract classes instead of interfaces? Sometimes. But your class may be a descendent of another class and in this case the interface is your only option.
302. How can you force garbage collection? You can't force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately.
303. How do you know if an explicit object casting is needed? If you assign a superclass object to a variable of a subclass's data type, you need to do explicit casting. For example:
Object a; Customer b; b = (Customer) a;
When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.
304. What's the difference between the methods sleep() and wait(). The code sleep(1000); puts thread aside for exactly one second. The code wait(1000), causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.
305. Can you write a Java class that could be used both as an applet as well as an application? Yes. Add a main() method to the applet.
306. What's the difference between constructors and other methods? Constructors must have the same name as the class and can not return a value. They are only called once while regular methods could be called many times.
307. Can you call one constructor from another if a class has multiple constructors. Yes. Use this() syntax.
308. Explain the usage of Java packages. This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.
309. If a class is located in a package, what do you need to change in the OS environment to be able to use it? You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Let's say a class Employee belongs to a package com.xyz.hr; and is located in the file c:\dev\com\xyz\hr\Employee.java. In this case, you'd need to add c:\dev to the variable CLASSPATH. If this class contains the method main(), you could test it from a command prompt window as follows:
c:\>java com.xyz.hr.Employee
310. What's the difference between J2SDK 1.5 and J2SDK 5.0? There's no difference, Sun Microsystems just re-branded this version.
311. What's the difference between a queue and a stack? Stacks works by last-in-first-out rule (LIFO), while queues use the FIFO rule.
312. Explain the usage of the keyword transient? This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers).
313. What comes to mind when you hear about a young generation in Java? Garbage collection.
314. What comes to mind when someone mentions a shallow copy in Java? Object cloning.
315. If you're overriding the method equals() of an object, which other method you might also consider? hashCode()
316. You are planning to do an indexed search in a list of objects. Which of the two Java collections should you use: ArrayList or LinkedList? ArrayList
317. What's the main difference between a Vector and ArrayList Java Vector class is internally synchronized and ArrayList is not.
318. When should the method invokeLater()be used? This method is used to ensure that Swing components are updated through the event-dispatching thread.
319. How would you make a copy of an entire Java object with its state? Have this class implement Cloneable interface and call its method clone().
320. What would you use to compare two String variables - the operator == or the method equals()? I'd use the method equals() to compare the values of the Strings and the == to check if two variables point at the same instance of a String object.
321. How can you minimize the need of garbage collection and make the memory use more effective? Use object pooling and weak object references.
322. How can a subclass call a method or a constructor defined in a superclass? Use the following syntax: super.myMethod(); To call a constructor of the superclass, just write super(); in the first line of the subclass's constructor.
323. There are two classes: A and B. The class B need to inform a class A when some important event has happened. What Java technique would you use to implement it? If these classes are threads I'd consider notify() or notifyAll(). For regular classes you can use the Observer interface.
324. What access level do you need to specify in the class declaration to ensure that only classes from the same directory can access it? You do not need to specify any access level, and Java will use a default package access level.
325. Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written? Yes, it does. The FileNoFoundException is inherited from the IOException. Exception's subclasses have to be caught first.
326. Can an inner class, declared inside of a method, access local variables of this method? It's possible only if these variables are final.
327. What can go wrong if you replace && with & in the following code:
String a=null; if (a!=null && a.length()>10) {...} A single ampersand here would lead to a NullPointerException.