Java interview questions part 7
Java interview questions part 7
Take as many assements as you can to improve your validate your skill rating
Total Questions: 20
1. Why are generics used?
Correct Answer is : Generics add stability to your code by making more of your bugs detectable at compile time
2. Which of these type parameters is used for a generic class to return and accept any type of object?
Correct Answer is : T
3. Which of these type parameters is used for a generic class to return and accept a number?
Correct Answer is : N
4. Which of these is an correct way of defining generic class?
Correct Answer is : class name { /* … */ }
5. Which of the following is an incorrect statement regarding the use of generics and parameterized types in Java?
Correct Answer is : When designing your own collections class (say, a linked list), generics and parameterized types allow you to achieve type safety with just a single class definition as opposed to defining multiple classes
6. Which of the following reference types cannot be generic?
Correct Answer is : Anonymous inner class
7. What is the output of this program?
public class BoxDemo
{
public static void addBox(U u, java.util.List> boxes)
{
Box box = new Box();
box.set(u);
boxes.add(box);
}
public static void outputBoxes(java.util.List> boxes)
{
int counter = 0;
for (Box box: boxes)
{
U boxContents = box.get();
System.out.println("Box #" + counter + " contains [" + boxContents.toString() + "]");
counter++;
}
}
public static void main(String[] args)
{
java.util.ArrayList> listOfIntegerBoxes = new java.util.ArrayList();
BoxDemo.addBox(Integer.valueOf(10), listOfIntegerBoxes);
BoxDemo.outputBoxes(listOfIntegerBoxes);
}
}
Correct Answer is : Box #0 contains [10].
8. What is the output of this program?
public class BoxDemo
{
public static void addBox(U u,
java.util.List> boxes)
{
Box box = new Box();
box.set(u);
boxes.add(box);
}
public static void outputBoxes(java.util.List> boxes)
{
int counter = 0;
for (Box box: boxes)
{
U boxContents = box.get();
System.out.println("[" + boxContents.toString() + "]");
counter++;
}
}
public static void main(String[] args)
{
java.util.ArrayList> listOfIntegerBoxes = new java.util.ArrayList();
BoxDemo.addBox(Integer.valueOf(0), listOfIntegerBoxes);
BoxDemo.outputBoxes(listOfIntegerBoxes);
}
}
Correct Answer is : [0].
9. What is the output of this program?
import java.util.*;
public class genericstack
{
Stack stk = new Stack ();
public void push(E obj)
{
stk.push(obj);
}
public E pop()
{
E obj = stk.pop();
return obj;
}
}
class Output
{
public static void main(String args[])
{
genericstack gs = new genericstack();
gs.push("Hello");
System.out.print(gs.pop() + " ");
genericstack gs = new genericstack();
gs.push(36);
System.out.println(gs.pop());
}
}
Correct Answer is : Hello 36
10. What is the output of this program?
public class BoxDemo
{
public static void addBox(U u,
java.util.List> boxes)
{
Box box = new Box();
box.set(u);
boxes.add(box);
}
public static void outputBoxes(java.util.List> boxes)
{
int counter = 0;
for (Box box: boxes)
{
U boxContents = box.get();
System.out.println("Box #" + counter + " contains [" + boxContents.toString() + "]");
counter++;
}
}
public static void main(String[] args)
{
java.util.ArrayList> listOfIntegerBoxes = new java.util.ArrayList();
BoxDemo.addBox(Integer.valueOf(10), listOfIntegerBoxes);
BoxDemo.outputBoxes(listOfIntegerBoxes);
}
}
Correct Answer is : Box #0 contains [10].
11. Which of the following access specifiers can be used for an interface?
Correct Answer is : Protected
12. Which of the following is the correct way of implementing an interface A by class B?
Correct Answer is : class B implements A{}
13. All methods must be implemented of an interface.
Correct Answer is : TRUE
14. What type of variable can be defined in an interface?
Correct Answer is : static final
15. What does an interface contain?
Correct Answer is : Method declaration
16. What type of methods an interface contain by default?
Correct Answer is : abstract
17. What will happen if we provide concrete implementation of method in interface?
Correct Answer is : Compilation failure
18. What happens when a constructor is defined for an interface?
Correct Answer is : Compilation failure
19. What happens when we access the same variable defined in two interfaces implemented by the same class?
Correct Answer is : The interfaceName.variableName needs to be defined
20. Can “abstract” keyword be used with constructor, Initialization Block, Instance Initialization and Static Initialization Block.
Correct Answer is : FALSE
