Java Interfaces And Abstract Classes MCQ - Quiz

Which of the following statements regarding abstract classes are true?
  • A An abstract class can be extended.
  • B A subclass of a non-abstract superclass can be abstract.
  • C A subclass can override a concrete method in a superclass to declare it abstract.
  • D All of the above 

interface Test{
      int p = 10; //line 1
      public int q = 20; //line 2
      public static int r = 30; //line 3
      public static final int s = 40; //line 4
}
Which of the above line will give compilation error?
  • A 1
  • B 2
  • C 3
  • D None of these

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

Given the following piece of code: 
public interface Guard{
        void doYourJob();
}
abstract public class Dog implements Guard{ }
which of the following statements is correct?
  • A This code will not compile, because method doYourJob() in interface Guard must be defined abstract.
  • B This code will not compile, because class Dog must implement method doYourJob() from interface Guard.
  • C This code will not compile, because in the declaration of class Dog we must use the keyword extends instead of implements.
  • D This code will compile without any errors.

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.

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

What will happen after compiling this program code? 
abstract class MyClass{ //line 1
      private int a, b;

      public void call(int a, int b){
            this.a = a;
            this.b = b;
            System.out.print(a+b);
      }
}

public class Test{
      public static void main(String args[]){
            MyClass m = new MyClass(); //line 2
            m.call(12,25);
      }
}

  • A Successful run and print 37
  • B Compilation error due to line 1
  • C Compilation error due to line 2
  • D Runtime error

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());
      }
}

  • A test-name
  • B Compilation fails due to an error on lines 1
  • C Compilation fails due to an error on lines 2
  • D Compilation succeed but Runtime Exception

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();
      }
}

  • A Program will compile and execute successfully and prints
  • B Compilation error as class can not be declared as abstract.
  • C Program compiles but leads to runtime exception.
  • D Compilation error occurs as the abstract class TestAbstract contains a non-abstract method.

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