JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

Which of the following statements regarding abstract classes are true?

All of these

An abstract class can be used as a data type.

A subclass of a non-abstract superclass can be abstract.

A subclass can override a concrete method in a superclass to declare it abstract.

An abstract class can be extended.

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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); }}

None of these

10

Runtime Exception

12

Compile with error

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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

None of these

Compilation error due to line 1

Runtime error

Compilation error due to line 2

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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. }

null

Compilation fails due to an error on line 8

Compilation fails due to an error on line 3

A

None of these

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In Java, declaring a class abstract is useful

To force developers to extend the class not to use its capabilities.

When default implementations of some methods are not desirable.

When it makes sense to have objects of that class.

When it doesn't make sense to have objects of that class.

To prevent developers from further extending the class.

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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

3

None of these

4

2

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Given the following piece of code:public class School{ public abstract double numberOfStudent();}which of the following statements is true?

The method numberOfStudent() in class School must have a body.

The keywords public and abstract cannot be used together.

Class School must be defined abstract.

You must add a return statement in method numberOfStudent().

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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 due to public modifier while declaring the display method.

The code will compile and execute successfully showing the output Welcome to Examians.

None of these

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 as the display method is not declared as abstract.

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Which of the following is a correct interface?

abstract interface A { print(); }

interface A { void print(); }

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

interface A { void print() { } }

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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

b is an instance of A followed by b is an instance of

b is an instance of

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