JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

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

2 and 3

2 and 4

3 and 4

1 and 2

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YOUR ANSWER : ?

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 default implementations of some methods are not desirable.

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

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

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What will be the output?interface A{public void method();}class One{public void method(){System.out.println("Class One method");}}class Two extends One implements A{public void method(){System.out.println("Class Two method");}}public class Test extends Two{public static void main(String[] args){A a = new Two();a.method();}}

will print Class Two method

compiles fine but print nothing

Compilation Error

None of these

will print Class One method

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Which of the following is a correct interface?

interface A { void print(); }

abstract interface A { print(); }

interface A { void print() { } }

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

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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

3 and 4

2 and 3

1 and 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); }}

Compile with error

None of these

10

Runtime Exception

12

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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 compile and execute successfully showing the output Welcome to Examians.

None of these

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

The code will lead to a compilation error as the display method is not declared as abstract.

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

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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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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 {}

1 and 2

3 and 6

2 and 4

3 and 5

5 and 6

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YOUR ANSWER : ?

Runnable is a _____ .

class

abstract class

interface

method

vaiable

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