Java Interfaces And Abstract Classes MCQ - Quiz

Which of the following is a correct interface?
  • A 
    interface A { void print() { } }
  • B 
     abstract interface A { print(); }
  • C 
    abstract interface A { abstract void print(); { }}
  • D 
     interface A { void print(); }

Runnable is a _____ .
  • A class
  • B abstract class
  • C interface
  • D vaiable

In Java, declaring a class abstract is useful
  • A To prevent developers from further extending the class.
  • B When it doesn't make sense to have objects of that class.
  • C When default implementations of some methods are not desirable.
  • D To force developers to extend the class not to use its capabilities.

Suppose A is an abstract class, B is a concrete subclass of A, and both A and B have a default constructor. Which of the following is correct?

1. A a = new A();
2. A a = new B();
3. B b = new A();
4. B b = new B();
  • A 1 and 2
  • B 2 and 4
  • C 3 and 4
  • D 1 and 3

What will be the output for the below code ? 
public interface TestInf{
      int i =10;
}

public class Test{
      public static void main(String... args){
            TestInf.i=12;
	    System.out.println(TestInf.i);
      }
}

  • A Compile with error
  • B 10
  • C 12
  • D Runtime Exception 

interface Base{
      boolean m1 ();
      byte m2(short s);
}
which two code fragments will compile? 
1. interface Base2 implements Base {}

2. abstract class Class2 extends Base
    { public boolean m1(){ return true; }}

3. abstract class Class2 implements Base {}

4. abstract class Class2 implements Base
    { public boolean m1(){ return (7 > 4); }}

5. abstract class Class2 implements Base
    { protected boolean m1(){ return (5 > 7) }}
  • A 1 and 2
  • B 2 and 3
  • C 3 and 4
  • D 1 and 3

What will be the output? 
interface A{
	public void method();
}
class One{
	public void method(){
		System.out.println("Class One method");
	}
}
class Two extends One implements A{
	public void method(){
		System.out.println("Class Two method");
	}
}
public class Test extends Two{
	public static void main(String[] args){
		A a = new Two();
		a.method();		
	}
}

  • A will print Class One method
  • B will print Class Two method
  • C compiles fine but print nothing
  • D Compilation Error

What happens if the following program is compiled and executed? 
interface MyInterface{
      void display();
}

interface MySubInterface extends MyInterface{
      void display();
}

public class Test implements MySubInterface{
      public void display(){
            System.out.print("Welcome to Examveda.");
      }
      public static void main(String args[]){
            Test t = new Test();
	    t.display();
      }
}

  • A The code will lead to a compilation error as declaration of the display method has been provided in two interface.
  • B The code will lead to a compilation error due to public modifier while declaring the display method.
  • C The code will compile and execute successfully showing the output Welcome to Examveda.
  • D The code will lead to a compilation error as the display method is not declared as abstract.

Given the following piece of code: 
public class School{
        public abstract double numberOfStudent();
}
which of the following statements is true?
  • A The keywords public and abstract cannot be used together.
  • B The method numberOfStudent() in class School must have a body.
  • C You must add a return statement in method numberOfStudent().
  • D Class School must be defined abstract.