Java Questions and Answers Part-12

1. Which of this keyword can be used in a subclass to call the constructor of superclass?
a) super
b) this
c) extent
d) extends

Answer: a

2. What is the process of defining a method in a subclass having same name & type signature as a method in its superclass?
a) Method overloading
b) Method overriding
c) Method hiding
d) None of the mentioned

Answer: b

3. Which of these keywords can be used to prevent Method overriding?
a) static
b) constant
c) protected
d) final

Answer: d
Explanation: To disallow a method from being overridden, specify final as a modifier at the start of its declaration. Methods declared as final cannot be overridden.

4. Which of these is correct way of calling a constructor having no parameters, of superclass A by subclass B?
a) super(void);
b) superclass.();
c) super.A();
d) super();

Answer: d

5. Choose 3 valid data-type attributes/qualifiers among “final, static, native, public, private, abstract, protected”
public interface Status
{
/* insert qualifier here */ int MY_VALUE = 10;
}
a) final, native, private
b) final, static, protected
c) final, private, abstract
d) final, static, public

Answer: d
Explanation: Every interface variable is implicitly public static and final.

6. Which of these is supported by method overriding in Java?
a) Abstraction
b) Encapsulation
c) Polymorphism
d) None of the mentioned

Answer: c

7. What will be the output of the following Java program?
class Alligator
{
public static void main(String[] args)
{
int []x[] = {{1,2}, {3,4,5}, {6,7,8,9}};
int [][]y = x;
System.out.println(y[2][1]);
}
}
a) 2
b) 3
c) 7
d) Compilation Error

Answer: c
Explanation: Both x,and y are pointing to the same array.

8. What will be the output of the following Java program?
final class A
{
int i;
}
class B extends A
{
int j;
System.out.println(j + " " + i);
}
class inheritance
{
public static void main(String args[])
{
B obj = new B();
obj.display();
}
}
a) 2 2
b) 3 3
c) Runtime Error
d) Compilation Error

Answer: d
Explanation: class A has been declared final hence it cannot be inherited by any other class. Hence class B does not have member i, giving compilation error.

9. What will be the output of the following Java program?
class Abc
{
public static void main(String[]args)
{
String[] elements = { "for", "tea", "too" };
String first = (elements.length > 0) ? elements[0]: null;
}
}
a) Compilation error
b) An exception is thrown at run time
c) The variable first is set to null
d) The variable first is set to elements[0]

Answer: d
Explanation: The value at the 0th position will be assigned to the variable first.

10. What will be the output of the following Java program?
class A
{
int i;
public void display()
{
System.out.println(i);
}
}
class B extends A
{
int j;
public void display()
{
System.out.println(j);
}
}
class Dynamic_dispatch
{
public static void main(String args[])
{
B obj2 = new B();
obj2.i = 1;
obj2.j = 2;
A r;
r = obj2;
r.display();
}
}
a) 1
b) 2
c) 3
d) 4

Answer: b
Explanation: r is reference of type A, the program assigns a reference of object obj2 to r and uses that reference to call function display() of class B.