JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

Which of the following is a correct interface?

interface A { void print() { } }

interface A { void print(); }

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

abstract interface A { print(); }

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

class A { abstract void unfinished() { } }

abstract class A { abstract void unfinished(); }

class A { abstract void unfinished(); }

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

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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) }}

2 and 3

1 and 3

4 and 5

1 and 2

3 and 4

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In Java, declaring a class abstract is useful

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

When it makes sense to have objects of that class.

To prevent developers from further extending the class.

When default implementations of some methods are not desirable.

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

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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();

3 and 4

1 and 2

1 and 3

2 and 3

2 and 4

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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

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

Program compiles but leads to runtime exception.

Compilation error as class can not be declared as abstract.

None of these

Program will compile and execute successfully and prints

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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); }}

Compile with error

Runtime Exception

12

10

None of these

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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 in the declaration of class Dog we must use the keyword extends instead of implements.

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

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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. }

A

Compilation fails due to an error on line 8

None of these

null

Compilation fails due to an error on line 3

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