JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

Runnable is a _____ .

class

interface

abstract class

vaiable

method

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YOUR ANSWER : ?

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); }}

Compilation error due to line 1

Successful run and print 37

None of these

Runtime error

Compilation error due to line 2

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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); }}

10

None of these

Runtime Exception

12

Compile with error

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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

A

None of these

null

Compilation fails due to an error on line 3

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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 A followed by b is an instance of

b is an instance of

Nothing.

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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 method doYourJob() in interface Guard must be defined abstract.

This code will compile without any errors.

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.

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Which of the following statements regarding abstract classes are true?

An abstract class can be used as a data type.

An abstract class can be extended.

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

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

All of these

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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.

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

Class School must be defined abstract.

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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();

2 and 4

1 and 3

2 and 3

1 and 2

3 and 4

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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()); }}

Compilation fails due to an error on lines 1

None of these

test-name

Compilation fails due to an error on lines 2

Compilation succeed but Runtime Exception

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