JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

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

public abstract void method() {}

public void abstract Method();

public void method() {}

public abstract method();

public abstract void method();

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YOUR ANSWER : ?

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

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

class A { abstract void unfinished() { } }

class A { abstract void unfinished(); }

abstract class A { abstract void unfinished(); }

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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();}}

Compilation Error

will print Class One method

compiles fine but print nothing

None of these

will print Class Two method

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YOUR ANSWER : ?

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

1 and 3

3 and 4

4 and 5

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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

3 and 4

1 and 3

2 and 3

1 and 2

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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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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

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

Nothing.

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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

Compilation fails due to an error on lines 2

Compilation succeed but Runtime Exception

None of these

test-name

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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(); }}

Program will compile and execute successfully and prints

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