Practice Interfaces And Abstract Classes Multiple Choice Questions with Answers Quiz-1

Q.1.

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. }

Compilation fails due to an error on line 3
A
Compilation fails due to an error on line 8
null
None of these

Explanation

Q.2.

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());
      }
}

test-name
Compilation fails due to an error on lines 2
Compilation fails due to an error on lines 1
Compilation succeed but Runtime Exception
None of these

Explanation

Q.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);
      }
}

Compile with error
10
12
Runtime Exception
None of these

Explanation

Q.4.

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();
      }
}

Program will compile and execute successfully and prints
Compilation error as class can not be declared as abstract.
Program compiles but leads to runtime exception.
Compilation error occurs as the abstract class TestAbstract contains a non-abstract method.
None of these

Explanation

Q.5.

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();
      }
}

The code will lead to a compilation error as declaration of the display method has been provided in two interface.
The code will lead to a compilation error due to public modifier while declaring the display method.
The code will compile and execute successfully showing the output Welcome to Examveda.
The code will lead to a compilation error as the display method is not declared as abstract.
None of these

Explanation

Q.6.

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) }}

1 and 2
2 and 3
3 and 4
1 and 3
4 and 5

Explanation

Q.7.

Which two of the following are legal declarations for abstract classes and interfaces?
1. final abstract class Test {}
2. public static interface Test {}
3. final public class Test {}
4. protected abstract class Test {}
5. protected interface Test {}
6. abstract public class Test {}

1 and 2
2 and 4
3 and 5
5 and 6
3 and 6

Explanation

Q.8.

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?

1
2
3
4
None of these

Q.9.

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);
      }
}

Successful run and print 37
Compilation error due to line 1
Compilation error due to line 2
Runtime error
None of these

Explanation

Q.10.

Runnable is a _____ .

class
abstract class
interface
vaiable
method

Q.11.

Which of the following is a correct interface?

interface A { void print() { } }
abstract interface A { print(); }
abstract interface A { abstract void print(); { }}
interface A { void print(); }

Q.12.

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");
        }
}

Nothing.
b is an instance of A.
b is an instance of C.
b is an instance of A followed by b is an instance of C.

Q.13.

Given the following piece of code:

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

which of the following statements is correct?

This code will not compile, because method doYourJob() in interface Guard must be defined abstract.
This code will not compile, because class Dog must implement method doYourJob() from interface Guard.
This code will not compile, because in the declaration of class Dog we must use the keyword extends instead of implements.
This code will compile without any errors.

Q.14.

In Java, declaring a class abstract is useful

To prevent developers from further extending the class.
When it doesn't make sense to have objects of that class.
When default implementations of some methods are not desirable.
To force developers to extend the class not to use its capabilities.
When it makes sense to have objects of that class.

Q.15.

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();		
	}
}

will print Class One method
will print Class Two method
compiles fine but print nothing
Compilation Error
None of these

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