Java MCQs on method overriding in Java Programming Language. 1. Which of this keyword can be used in a subclass to call the constructor of superclass?
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? Answer: b 3. Which of these keywords can be used to prevent Method overriding? Answer: d 4. Which of these is correct way of calling a constructor having no parameters, of superclass A by subclass B? Answer: d 5.
At line number 2 in the following code, choose 3 valid data-type attributes/qualifiers among “final, static, native, public, private, abstract, protected”
a) super
b) this
c) extent
d) extends
Clarification: None.
a) Method overloading
b) Method overriding
c) Method hiding
d) None of the mentioned
Clarification: None.
a) static
b) constant
c) protected
d) final
Clarification: 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.
a) super(void);
b) superclass.();
c) super.A();
d) super();
Clarification: None.
a) final, native, private
b) final, static, protected
c) final, private, abstract
d) final, static, public
Answer: d
Clarification: 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
Clarification: None.
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
Clarification: 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
Clarification: 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.
output:
$ javac inheritance.java Exception in thread "main" java.lang.Error: Unresolved compilation problem: i cannot be resolved or is not a field
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
Clarification: 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
Clarification: 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.
output:
$ javac Dynamic_dispatch.java $ java Dynamic_dispatch 2