Java Interfaces And Abstract Classes MCQ - Quiz

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: Given the following piece of code:

public class School{
        public abstract double numberOfStudent();
}

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: In Java, declaring a class abstract is useful

Q: 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();		
	}
}

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 will be the output when the following program is compiled and executed?

abstract class TestAbstract{
      String my_name;
      String myName(){
            my_name = "Examveda";
            return my_name;
      }
      abstract void display();
}

public class Test extends TestAbstract{
      void display(){
            String n = myName();
	    System.out.print("My name is "+ n);
      }

      public static void main(String args[]){
            Test t = new Test();
	    t.display();
      }
}

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();
      }
}