Java Interview Questions :: Challenging all Java Developers

[javaguru]

Hi all Java developers of abhisays.com Discussion zone. I am starting a new thread of Java interview questions.. I will ask small questions and you have to answer.. The person who will answer maximum number of questions correctly will be awarded the title of Java Geek.. Let's start the quiz..and best of luck to all members..

Which programming language was the main inspiration behind the development of Java?

[umesh]

Java is inspired from smalltalk, one of the first object oriented programming languages..

[sony]

Now my question.. what are marker interfaces and its advantages? Why we use marker interfaces?

[abhishek]

A so-called marker interface is a Java interface which doesn't actually define any fields. It is just used to "mark" Java classes which support a certain capability -- the class marks itself as implementing the interface.

There are few Java supplied marker interfaces like Cloneable, Serializable, etc. One can create their own marker interfaces the same way as they create any other interface in Java.

The main purpose to have marker interfaces is to create special types in those cases where the types themselves have no behavior particular to them. If there is no behavior then why to have an interface?

Because the implementor of the class might only need to flag that it belongs to that particular type and everything else is handled/done by some other unit - either internal to Java (as in the case of Java supplied standard marker interfaces) or an app specific external unit.

[rambler]

My question..

When destory method is called in servlet life cycle?

[shefali]

The destroy() method is usually called by the servlet container immediately before it takes a servlet out of service. It is typically used to clean-up any resource references, save temporary data and suchlike. For example, it is called during server restart..

[abhishek]

Next question.. What is the difference between call by value and call by reference?

[sunita]

The arguments passed to function can be of two types namely



1. Values passed
2. Address passed



The first type refers to call by value and the second type refers to call by reference.



For instance consider program1

main() 
{ 
int x=50, y=70; 
interchange(x,y); 
printf(“x=%d y=%d”,x,y); 
} 

interchange(x1,y1) 
int x1,y1; 
{ 
int z1; 
z1=x1; 
x1=y1; 
y1=z1; 
printf(“x1=%d y1=%d”,x1,y1); 
}

Here the value to function interchange is passed by value.



Consider program2

main() 
{ 
int x=50, y=70; 
interchange(&x,&y); 
printf(“x=%d y=%d”,x,y); 
} 

interchange(x1,y1) 
int *x1,*y1; 
{ 
int z1; 
z1=*x1; 
*x1=*y1; 
*y1=z1; 
printf(“*x=%d *y=%d”,x1,y1); 
}

Here the function is called by reference. In other words address is passed by using symbol & and the value is accessed by using symbol *.



The main difference between them can be seen by analyzing the output of program1 and program2.



The output of program1 that is call by value is



x1=70 y1=50
x=50 y=70



But the output of program2 that is call by reference is



*x=70 *y=50
x=70 y=50



This is because in case of call by value the value is passed to function named as interchange and there the value got interchanged and got printed as



x1=70 y1=50



and again since no values are returned back and therefore original values of x and y as in main function namely



x=50 y=70 got printed.

[abhishek]

nice explanation with examples.. thanks for sharing.. Next question please..

[swati.]

Next question from my side.

What are wrapper classes in Java?