~~~Hello World~~~: October 2010

Saturday, October 23, 2010

Operating System..

Hi...Anyone can post answers for the frequently asking possible OS questions here...

· What is MUTEX ?
· What isthe difference between a 'thread' and a 'process'?
· What is INODE?
· Explain the working of Virtual Memory.
· How does Windows NT supports Multitasking?
· Explain the Unix Kernel.
· What is Concurrency? Expain with example Deadlock and Starvation.
· What are your solution strategies for "Dining Philosophers Problem" ?
· Explain Memory Partitioning, Paging, Segmentation.
· Explain Scheduling.
· Operating System Security.
· What is Semaphore?
· Explain the following file systems : NTFS, Macintosh(HPFS), FAT .
· What are the different process states?
· What is Marshalling?
· Define and explain COM?
· What is Marshalling?
· Difference - Loading and Linking ?
· What are the basic functions of an operating system?
· Explain briefly about, processor, assembler, compiler, loader, linker and the functions executed by them.
· What are the difference phases of software development? Explain briefly?
· Differentiate between RAM and ROM?
· What is DRAM? In which form does it store data?
· What is cache memory?
· What is hard disk and what is its purpose?
· Differentiate between Complier and Interpreter?
· What are the different tasks of Lexical analysis?
· What are the different functions of Syntax phase, Sheduler?
· What are the main difference between Micro-Controller and Micro- Processor?
· Describe different job scheduling in operating systems.
· What is a Real-Time System ?
· What is the difference between Hard and Soft real-time systems ?
· What is a mission critical system ?
· What is the important aspect of a real-time system ?
· If two processes which shares same system memory and system clock in a distributed system, What is it called?
· What is the state of the processor, when a process is waiting for some event to occur?
· What do you mean by deadlock?
· Explain the difference between microkernel and macro kernel.
· Give an example of microkernel.
· When would you choose bottom up methodology?
· When would you choose top down methodology?
· Write a small dc shell script to find number of FF in the design.
· Why paging is used ?
· Which is the best page replacement algorithm and Why? How much time is spent usually in each phases and why?
· Difference between Primary storage and secondary storage?
· What is multi tasking, multi programming, multi threading?
· Difference between multi threading and multi tasking?
· What is software life cycle?
· Demand paging, page faults, replacement algorithms, thrashing, etc.
· Explain about paged segmentation and segment paging
· While running DOS on a PC, which command would be used to duplicate the entire diskette?

C++ interview question

1) What are the things contains in .obj file ? ( compiled result of .cpp file )
Answer :C++ .obj file holds code and data suitable for linking with other object files to create an executable or a shared object file.

2)What is difference between followin intialization.
int iVar1;
int iVar2 = int();
and which one of two should we prefer always and why?
Answer :In first case a variable will be create in memeory with the default base type value (depending upon compiler 2 compiler) bcoz it is not initialized. in second case the variable will be created in the memory with the value retuned by the function int() (if int is a user define function) the second statement should have been int *i = new int();

3)What is the difference between Object and Instance?
Answer :An instance of a user-defined type (i.e., a class) is called an object. We can instantiate many objects from one class.An object is an instance or occurrence of a class.

4) How is static variable stored in the memory?
(if there are 2 functions in a file, and the static variable name is same (ex var) in both the function. how is it keep separately in the memory).
Answer: C++ uses name mangling when storing both local and global static varibales at the same place. The local static variables have function name and the global variables will have file name. Essentially the compiler uses namespace to distinguish between local and global static variables.

5)what is the difference betwen wait() and delay()?
Answer :Wait() and delay() works same but works on different platforms. Wait(2) will wait processing fro 2 second on Linux/Unix while delay(2000) with wait for 2 second but on DOS or Windows. so wait(2) on linux == delay(2000) on DOS Delay() is under while one can directly use wait in his/her program.

C Puzzles

1.The expected output of the following C program is to print the elements in the array. But when actually run, it doesn't do so.
#include
#define TOTAL_ELEMENTS (sizeof(array) / sizeof(array[0]))
int array[] = {23,34,12,17,204,99,16};
int main()
{
int d;
for(d=-1;d <= (TOTAL_ELEMENTS-2);d++)
printf("%d\n",array[d+1]);
return 0;
}
Find out what's going wrong.

Hint :Catch Ur Hint Here...!!

2.I thought the following program was a perfect C program. But on compiling, I found a silly mistake. Can you find it out (without compiling the program :-) ?
#include

void OS_Solaris_print()
{
printf("Solaris - Sun Microsystems\n");
}

void OS_Windows_print()
{
printf("Windows - Microsoft\n");

}
void OS_HP-UX_print()
{
printf("HP-UX - Hewlett Packard\n");
}

int main()
{
int num;
printf("Enter the number (1-3):\n");
scanf("%d",&num);
switch(num)
{
case 1:
OS_Solaris_print();
break;
case 2:
OS_Windows_print();
break;
case 3:
OS_HP-UX_print();
break;
default:
printf("Hmm! only 1-3 :-)\n");
break;
}

return 0;
}

Hint: Catch Ur Hint Here !!

3.What's the expected output for the following program and why?
enum {false,true};

int main()
{
int i=1;
do
{
printf("%d\n",i);
i++;
if(i < 15)
continue;
}while(false);
return 0;
}

Hint: Catch Ur Hint Here !!

C Aptitude Questions With Explanations

1.    void main()
{
            int const * p=5;
            printf("%d",++(*p));
}

Answer:
Compiler error: Cannot modify a constant value.
Explanation:
p is a pointer to a "constant integer". But we tried to change the value of the "constant integer".

2.    main()
{
            char s[ ]="man";
            int i;
            for(i=0;s[ i ];i++)
            printf("\n%c%c%c%c",s[ i ],*(s+i),*(i+s),i[s]);
}

Answer:
                        mmmm
                       aaaa
                       nnnn
Explanation:
s[i], *(i+s), *(s+i), i[s] are all different ways of expressing the same idea. Generally array name is the base address for that array. Here s is the base address. i is the index number/displacement from the base address. So, indirecting it with * is same as s[i]. i[s] may be surprising. But in the case of C it is same as s[i].

3.      main()
{
            float me = 1.1;
            double you = 1.1;
            if(me==you)
printf("I love U");
else
                        printf("I hate U");
}

Answer:
I hate U

Explanation:
For floating point numbers (float, double, long double) the values cannot be predicted exactly. Depending on the number of bytes, the precession with of the value represented varies. Float takes 4 bytes and long double takes 10 bytes. So float stores 0.9 with less precision than long double.
Rule of Thumb:
Never compare or at-least be cautious when using floating point numbers with relational operators (== , >, <, <=, >=,!= ) .

4.      main()
            {
            static int var = 5;
            printf("%d ",var--);
            if(var)
                        main();
            }

Answer:
5 4 3 2 1

Explanation:
When static storage class is given, it is initialized once. The change in the value of a static variable is retained even between the function calls. Main is also treated like any other ordinary function, which can be called recursively.

5.      main()
{
            int c[ ]={2.8,3.4,4,6.7,5};
            int j,*p=c,*q=c;
            for(j=0;j<5;j++) {
                        printf(" %d ",*c);
                        ++q;     }
            for(j=0;j<5;j++){
printf(" %d ",*p);
++p;     }
}

Answer:
                        2 2 2 2 2 2 3 4 6 5

Explanation:
Initially pointer c is assigned to both p and q. In the first loop, since only q is incremented and not c , the value 2 will be printed 5 times. In second loop p itself is incremented. So the values 2 3 4 6 5 will be printed.

6.      main()
{
            extern int i;
            i=20;
printf("%d",i);
}

Answer:
Linker Error : Undefined symbol '_i'
Explanation:
                        extern storage class in the following declaration,
                                    extern int i;
specifies to the compiler that the memory for i is allocated in some other program and that address will be given to the current program at the time of linking. But linker finds that no other variable of name i is available in any other program with memory space allocated for it. Hence a linker error has occurred .

7.      main()
{
            int i=-1,j=-1,k=0,l=2,m;
            m=i++&&j++&&k++||l++;
            printf("%d %d %d %d %d",i,j,k,l,m);
}

Answer:
                        0 0 1 3 1

Explanation :
Logical operations always give a result of 1 or 0 . And also the logical AND (&&) operator has higher priority over the logical OR (||) operator. So the expression ‘i++ && j++ && k++’ is executed first. The result of this expression is 0    (-1 && -1 && 0 = 0). Now the expression is 0 || 2 which evaluates to 1 (because OR operator always gives 1 except for ‘0 || 0’ combination- for which it gives 0). So the value of m is 1. The values of other variables are also incremented by 1.

8.      main()
{
            char *p;
            printf("%d %d ",sizeof(*p),sizeof(p));
}

Answer:
                        1 2

Explanation:
The sizeof() operator gives the number of bytes taken by its operand. P is a character pointer, which needs one byte for storing its value (a character). Hence sizeof(*p) gives a value of 1. Since it needs two bytes to store the address of the character pointer sizeof(p) gives 2.

9.      main()
{
            int i=3;
            switch(i)
            {
                default:printf("zero");
                case 1: printf("one");
                           break;
               case 2:printf("two");
                          break;
              case 3: printf("three");
                          break;
              }
}

Answer :
three

Explanation :
The default case can be placed anywhere inside the loop. It is executed only when all other cases doesn't match.

10. main()
{
printf("%x",-1<<4);
}

Answer:
fff0

Explanation :
-1 is internally represented as all 1's. When left shifted four times the least significant 4 bits are filled with 0's.The %x format specifier specifies that the integer value be printed as a hexadecimal value.

11.      main()
{
            char string[]="Hello World";
            display(string);
}
void display(char *string)
{
            printf("%s",string);
}

Answer:
Compiler Error : Type mismatch in redeclaration of function display

Explanation :
In third line, when the function display is encountered, the compiler doesn't know anything about the function display. It assumes the arguments and return types to be integers, (which is the default type). When it sees the actual function display, the arguments and type contradicts with what it has assumed previously. Hence a compile time error occurs.

12.      main()
{
            int c=- -2;
            printf("c=%d",c);
}

Answer:
                                    c=2;

Explanation:
Here unary minus (or negation) operator is used twice. Same maths rules applies, ie. minus * minus= plus.
Note:
However you cannot give like --2. Because -- operator can only be applied to variables as a decrement operator (eg., i--). 2 is a constant and not a variable.
13.      #define int char
main()
{
            int i=65;
            printf("sizeof(i)=%d",sizeof(i));
}

Answer:
                        sizeof(i)=1

Explanation:
Since the #define replaces the string int by the macro char
14.      main()
{
int i=10;
i=!i>14;
Printf ("i=%d",i);
}

Answer:
i=0

Explanation:
In the expression !i>14 , NOT (!) operator has more precedence than ‘ >’ symbol. ! is a unary logical operator. !i (!10) is 0 (not of true is false). 0>14 is false (zero).

15. #include
main()
{
char s[]={'a','b','c','\n','c','\0'};
char *p,*str,*str1;
p=&s[3];
str=p;
str1=s;
printf("%d",++*p + ++*str1-32);
}

Answer:
77

Explanation:
p is pointing to character '\n'. str1 is pointing to character 'a' ++*p. "p is pointing to '\n' and that is incremented by one." the ASCII value of '\n' is 10, which is then incremented to 11. The value of ++*p is 11. ++*str1, str1 is pointing to 'a' that is incremented by 1 and it becomes 'b'. ASCII value of 'b' is 98.
Now performing (11 + 98 – 32), we get 77("M");
So we get the output 77 :: "M" (Ascii is 77).

Friday, October 22, 2010

Interview Questions on Java

1.What if the main method is declared as private?

The program compiles properly but at runtime it will give "Main method not public." message.

2.What is meant by pass by reference and pass by value in Java?

Pass by reference means, passing the address itself rather than passing the value. Pass by value means
passing a copy of the value.

3.If you're overriding the method equals() of an object, which other method you might also consider?

hashCode()

4.What is Byte Code?

What gives java it's "write once and run anywhere" nature?

All Java programs are compiled into class files that contain bytecodes. These byte codes can be run in any platform and hence java is said to be platform independent.

5.Expain the reason for each keyword of public static void main(String args[])?

public- main(..) is the first method called by java environment when a program is executed so it has to accessible from java environment. Hence the access specifier has to be public.

static: Java environment should be able to call this method without creating an instance of the class , so this method must be declared as static.

void: main does not return anything so the return type must be void

The argument String indicates the argument type which is given at the command line and arg is an array for string given during command line.

6.What are the differences between == and .equals() ?

what is difference between == and equals

Difference between == and equals method

What would you use to compare two String variables - the operator == or the method equals()?

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 i.e. present in the same memory location. It is possible for two String objects to have the same value, but located in different areas of memory.

== compares references while .equals compares contents. The method public boolean equals(Object obj) is provided by the Object class and can be overridden. The default implementation returns true only if the object is compared with itself, which is equivalent to the equality operator == being used to compare aliases to the object. String, BitSet, Date, and File override the equals() method. For two String objects, value equality means that they contain the same character sequence. For the Wrapper classes, value equality means that the primitive values are equal. public class EqualsTest {

public static void main(String[] args) {

String s1 = "abc";

String s2 = s1;

String s5 = "abc";

String s3 = new String("abc");

String s4 = new String("abc");

System.out.println("== comparison : " + (s1 == s5));

System.out.println("== comparison : " + (s1 == s2));

System.out.println("Using equals method : " + s1.equals(s2));

System.out.println("== comparison : " + s3 == s4);

System.out.println("Using equals method : " + s3.equals(s4));

}

Output

== comparison : true

Using equals method : true

false

Using equals method : true

7.What if the static modifier is removed from the signature of the main method?

What if I do not provide the String array as the argument to the method?

Program compiles. But at runtime throws an error "NoSuchMethodError".

8.Why oracle Type 4 driver is named as oracle thin driver?

Oracle provides a Type 4 JDBC driver, referred to as the Oracle "thin" driver. This driver includes its own implementation of a TCP/IP version of Oracle's Net8 written entirely in Java, so it is platform independent, can be downloaded to a browser at runtime, and does not require any Oracle software on the client side. This driver requires a TCP/IP listener on the server side, and the client connection string uses the TCP/IP port address, not the TNSNAMES entry for the database name.

9.What is the difference between final, finally and finalize? What do you understand by the java final keyword?

What is final, finalize() and finally?

What is finalize() method?

What is the difference between final, finally and finalize?

What does it mean that a class or member is final?

o final - declare constant

o finally - handles exception

o finalize - helps in garbage collection

Variables defined in an interface are implicitly final. A final class can't be extended i.e., final class may not be subclassed. This is done for security reasons with basic classes like String and Integer. It also allows the compiler to make some optimizations, and makes thread safety a little easier to achieve. A final method can't be overridden when its class is inherited. You can't change value of a final variable (is a constant). finalize() method is used just before an object is destroyed and garbage collected. finally, a key word used in exception handling and will be executed whether or not an exception is thrown. For example, closing of open connections is done in the finally method.

10.What is the Java API?

The Java API is a large collection of ready-made software components that provide many useful capabilities, such as graphical user interface (GUI) widgets.

11.What is the GregorianCalendar class?

The GregorianCalendar provides support for traditional Western calendars.

12.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.

13.Why there are no global variables in Java?

Global variables are globally accessible. Java does not support globally accessible variables due to following reasons:

The global variables breaks the referential transparency

Global variables creates collisions in namespace.

14.How to convert String to Number in java program?

The valueOf() function of Integer class is is used to convert string to Number. Here is the code example:

String numString = "1000″;

int id=Integer.valueOf(numString).intValue();

15.What is the SimpleTimeZone class?

The SimpleTimeZone class provides support for a Gregorian calendar.

16.What is the difference between a while statement and a do statement?

A while statement (pre test) checks at the beginning of a loop to see whether the next loop iteration should occur. A do while statement (post test) 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 loop body at least once.

17.What is the Locale class?

The Locale class is used to tailor a program output to the conventions of a particular geographic, political, or cultural region.

18.Describe the principles of OOPS.

There are three main principals of oops which are called Polymorphism, Inheritance and Encapsulation.

19.Explain the Inheritance principle.

Inheritance is the process by which one object acquires the properties of another object. Inheritance allows well-tested procedures to be reused and enables changes to make once and have effect in all relevant places

20.What is implicit casting?

Implicit casting is the process of simply assigning one entity to another without any transformation guidance to the compiler. This type of casting is not permitted in all kinds of transformations and may not work for all scenarios.

Example

int i = 1000;

long j = i; //Implicit casting

21.Is sizeof a keyword in java?

The sizeof operator is not a keyword.

22.What is a native method?

A native method is a method that is implemented in a language other than Java.

23.In System.out.println(), what is System, out and println?

System is a predefined final class, out is a PrintStream object and println is a built-in overloaded method in the out object.

24.What is explicit casting?

Explicit casting in the process in which the complier are specifically informed to about transforming the object.

Example

long i = 700.20;

int j = (int) i; //Explicit casting

25.What is the Java Virtual Machine (JVM)?

The Java Virtual Machine is software that can be ported onto various hardware-based platforms

Basic Java interview questions

What is a Marker Interface? - An interface with no methods. Example: Serializable, Remote, Cloneable
What interface do you implement to do the sorting? - Comparable
What is the eligibility for a object to get cloned? - It must implement the Cloneable interface
What is the purpose of abstract class? - It is not an instantiable class. It provides the concrete implementation for some/all the methods. So that they can reuse the concrete functionality by inheriting the abstract class.
What is the difference between interface and abstract class? - Abstract class defined with methods. Interface will declare only the methods. Abstract classes are very much useful when there is a some functionality across various classes. Interfaces are well suited for the classes which varies in functionality but with the same method signatures.
What do you mean by RMI and how it is useful? - RMI is a remote method invocation. Using RMI, you can work with remote object. The function calls are as though you are invoking a local variable. So it gives you a impression that you are working really with a object that resides within your own JVM though it is somewhere.
What is the protocol used by RMI? - RMI-IIOP
What is a hashCode? - hash code value for this object which is unique for every object.
What is a thread? - Thread is a block of code which can execute concurrently with other threads in the JVM.
What is the algorithm used in Thread scheduling? - Fixed priority scheduling.
What is hash-collision in Hashtable and how it is handled in Java? - Two different keys with the same hash value. Two different entries will be kept in a single hash bucket to avoid the collision.
What are the different driver types available in JDBC? - 1. A JDBC-ODBC bridge 2. A native-API partly Java technology-enabled driver 3. A net-protocol fully Java technology-enabled driver 4. A native-protocol fully Java technology-enabled driver For more information: Driver Description
Is JDBC-ODBC bridge multi-threaded? - No
Does the JDBC-ODBC Bridge support multiple concurrent open statements per connection? - No
What is the use of serializable? - To persist the state of an object into any perminant storage device.
What is the use of transient? - It is an indicator to the JVM that those variables should not be persisted. It is the users responsibility to initialize the value when read back from the storage.
What are the different level lockings using the synchronization keyword? - Class level lock Object level lock Method level lock Block level lock
What is the use of preparedstatement? - Preparedstatements are precompiled statements. It is mainly used to speed up the process of inserting/updating/deleting especially when there is a bulk processing.
What is callable statement? Tell me the way to get the callable statement? - Callablestatements are used to invoke the stored procedures. You can obtain the callablestatement from Connection using the following methods prepareCall(String sql) prepareCall(String sql, int resultSetType, int resultSetConcurrency)
In a statement, I am executing a batch. What is the result of the execution? - It returns the int array. The array contains the affected row count in the corresponding index of the SQL.
Can a abstract method have the static qualifier? - No
What are the different types of qualifier and what is the default qualifier? - public, protected, private, package (default)
What is the super class of Hashtable? - Dictionary
What is a lightweight component? - Lightweight components are the one which doesn’t go with the native call to obtain the graphical units. They share their parent component graphical units to render them. Example, Swing components
What is a heavyweight component? - For every paint call, there will be a native call to get the graphical units. Example, AWT.
What is an applet? - Applet is a program which can get downloaded into a client environment and start executing there.
What do you mean by a Classloader? - Classloader is the one which loads the classes into the JVM.
What are the implicit packages that need not get imported into a class file? - java.lang
What is the difference between lightweight and heavyweight component? - Lightweight components reuses its parents graphical units. Heavyweight components goes with the native graphical unit for every component. Lightweight components are faster than the heavyweight components.
What are the ways in which you can instantiate a thread? - Using Thread class By implementing the Runnable interface and giving that handle to the Thread class.
What are the states of a thread? - 1. New 2. Runnable 3. Not Runnable 4. Dead
What is a socket? - A socket is an endpoint for communication between two machines.
How will you establish the connection between the servlet and an applet? - Using the URL, I will create the connection URL. Then by openConnection method of the URL, I will establish the connection, through which I can be able to exchange data.
What are the threads will start, when you start the java program? - Finalizer, Main, Reference Handler, Signal Dispatcher