JAVA INTERFACES AND ABSTRACT CLASSES QUIZ

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.

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

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

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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?

None of these

4

3

1

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); }}

None of these

Compile with error

12

10

Runtime Exception

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

Compilation error as class can not be declared as abstract.

Program will compile and execute successfully and prints

Program compiles but leads to runtime exception.

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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) }}

4 and 5

2 and 3

1 and 2

3 and 4

1 and 3

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

abstract class A { abstract void unfinished(); }

class A { abstract void unfinished() { } }

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

class A { abstract void unfinished(); }

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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

b is an instance of

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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 compile without any errors.

This code will not compile, because in the declaration of class Dog we must use the keyword extends instead of implements.

This code will not compile, because method doYourJob() in interface Guard must be defined abstract.

This code will not compile, because class Dog must implement method doYourJob() from interface Guard.

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

public abstract void method() {}

public void abstract Method();

public abstract void method();

public void method() {}

public abstract method();

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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

2 and 3

3 and 4

1 and 2

1 and 3

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