Java Interfaces And Abstract Classes MCQ - Quiz

Q: Which of the following class definitions defines a legal abstract class?

Q: Which of the following statements regarding abstract classes are true?

Q: 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();

Q: Which of the following is a correct interface?

Q: Determine output of the following code.

interface A { }

class C { }

class D extends C { }

class B extends D implements A { }

public class Test extends Thread{
        public static void main(String[] args){
                B b = new B();
                if (b instanceof A)
                        System.out.println("b is an instance of A");
                if (b instanceof C)
                        System.out.println("b is an instance of C");
        }
}

Q: Given the following piece of code:

public interface Guard{
        void doYourJob();
}
abstract public class Dog implements Guard{ }

Q:

interface Base{
      boolean m1 ();
      byte m2(short s);
}

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) }}

Q: What is the output for the below code ?

interface A{
      public void printValue();
}

1. public class Test{
2.       public static void main (String[] args){
3.             A a1 = new A(){
4.                          public void printValue(){
5.                                System.out.println("A");
6.                          }
7.                    };
8.             a1.printValue();
9.       }
10. }

Q: What will be the output?

1. public interface InfA{
2.       protected String getName();
3. }

public class Test implements InfA{
      public String getName(){
            return "test-name";
      }
      public static void main (String[] args){
            Test t = new Test();
            System.out.println(t.getName());
      }
}

Q: 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();
      }
}