JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

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

public abstract void method() {}

public abstract method();

public void abstract Method();

public abstract void method();

public void method() {}

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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 2

2 and 3

4 and 5

1 and 3

3 and 4

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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 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().

Class School must be defined abstract.

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

class A { abstract void unfinished() { } }

class A { abstract void unfinished(); }

abstract class A { abstract void unfinished(); }

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

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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?

2

4

None of these

1

3

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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 {}

2 and 4

5 and 6

3 and 5

1 and 2

3 and 6

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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 succeed but Runtime Exception

None of these

Compilation fails due to an error on lines 2

Compilation fails due to an error on lines 1

test-name

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

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.

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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 3

2 and 4

1 and 2

3 and 4

2 and 3

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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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