JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

Which of the following is a correct interface?

interface A { void print(); }

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

interface A { void print() { } }

abstract interface A { print(); }

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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 class Dog must implement method doYourJob() from interface Guard.

This code will compile without any errors.

This code will not compile, because in the declaration of class Dog we must use the keyword extends instead of implements.

This code will not compile, because method doYourJob() in interface Guard must be defined abstract.

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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) }}

3 and 4

4 and 5

1 and 3

2 and 3

1 and 2

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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.

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.

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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 keywords public and abstract cannot be used together.

Class School must be defined abstract.

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

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

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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. }

None of these

Compilation fails due to an error on line 3

Compilation fails due to an error on line 8

null

A

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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"); }}

b is an instance of

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

Nothing.

b is an instance of

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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 as the display method is not declared as abstract.

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

The code will lead to a compilation error due to public modifier while declaring the display method.

None of these

The code will lead to a compilation error as declaration of the display method has been provided in two interface.

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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();

1 and 3

1 and 2

3 and 4

2 and 3

2 and 4

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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 {}

2 and 4

5 and 6

1 and 2

3 and 6

3 and 5

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