JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

Which of the following declares an abstract method in an abstract Java class?

public abstract void method() {}

public void method() {}

public void abstract Method();

public abstract void method();

public abstract method();

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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. }

Compilation fails due to an error on line 8

None of these

A

Compilation fails due to an error on line 3

null

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Runnable is a _____ .

class

method

vaiable

interface

abstract 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?

None of these

3

4

2

1

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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(); }}

Compilation error as class can not be declared as abstract.

Compilation error occurs as the abstract class TestAbstract contains a non-abstract method.

Program will compile and execute successfully and prints

Program compiles but leads to runtime exception.

None of these

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In Java, declaring a class abstract is useful

When default implementations of some methods are not desirable.

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

To prevent developers from further extending the class.

When it makes sense to have objects of that class.

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

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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 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.

This code will compile without any errors.

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Which of the following class definitions defines a legal abstract class?

class A { abstract void unfinished(); }

public class abstract A { abstract void unfinished(); }

class A { abstract void unfinished() { } }

abstract class A { abstract void unfinished(); }

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

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

The keywords public and abstract cannot be used together.

Class School must be defined abstract.

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

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

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

An abstract class can be extended.

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