JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

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

public void method() {}

public abstract void method();

public void abstract Method();

public abstract void method() {}

public abstract method();

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In Java, declaring a class abstract is useful

To prevent developers from further extending the class.

When it makes sense to have objects of that 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.

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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

Nothing.

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

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

Class School must be defined abstract.

The keywords public and abstract cannot be used together.

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

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

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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) }}

1 and 3

4 and 5

1 and 2

2 and 3

3 and 4

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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(); }}

None of these

Compilation error as class can not be declared as abstract.

Program compiles but leads to runtime exception.

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

Program will compile and execute successfully and prints

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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 2

2 and 3

3 and 4

2 and 4

1 and 3

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Runnable is a _____ .

class

abstract class

method

interface

vaiable

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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); }}

None of these

Successful run and print 37

Compilation error due to line 2

Runtime error

Compilation error due to line 1

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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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