CAI710 - Inheritance

A car dealership needs a program to store information about the cars for sale. For each car, they want to keep track of the following information: number of doors (2 or 4), whether the car has air conditioning, and its average number of miles per gallon. Which of the following is the best object-oriented program design?

• Use one class, Car, with three instance variables:

  int numDoors, boolean hasAir, and

  double milesPerGallon

• Use four unrelated classes: Car, Doors, AirConditioning, and MilesPerGallon.

• Use a class Car with three subclasses: Doors, AirConditioning, and MilesPerGallon.

• Use a class Car, with a subclass Doors, with a subclass

  AirConditioning, with a subclass MilesPerGallon.

• Use three classes: Doors, AirConditioning, and MilesPerGallon, each with a subclass Car.

Consider the following class definitions.

public class ClassA

{

public String getValue()

{

return "A";

}

public void showValue()

{

System.out.print(getValue());

}

}

public class ClassB extends ClassA

{

public String getValue()

{

return "B";

}

}

The following code segment appears in a class other than ClassA or ClassB.

ClassA obj = new ClassB();

obj.showValue();

What, if anything, is printed when the code segment is executed?

• A

• B

• AB

• BA

• Nothing

The following Syntax is used for?

class Subclass-name extends Superclass-name

{

//methods and fields

}

• Polymorphism

• Encapsulation

• Inheritance

• Incorrect syntax

A class that is inherited is called a ______ .

• Subclass

• SetClass

• SuperClass

• Child Class

Which Java statement represents inheritance?

• Class Car inherits Vehicle

• Class Car inherits Super Vehicle

• Class Car Super Vehicle

• Class Car extends Vehicle

• Class Car Override Vehicle

Which of the following is/are false about inheritance in Java?

I. A subclass inherits all the methods and variables of the superclass.

II. A subclass can override the methods of its superclass

III. A subclass has access to the private instance variables of the superclass.

• I only

• II only

• III only

• I and II only

• I, II and III only

Consider the following code.

class Vehicle

{

int maxSpeed = 120;

}

class Car extends Vehicle

{

int maxSpeed = 180;

void display() {

System.out.println("Maximum Speed: " + super.maxSpeed);

}

}

/* Driver program to test */

class Test

{

public static void main(String[] args)

{

Car small = new Car(); small.display();

}

}

In the program output, what is the maximum speed displayed?

• 120

• 180

• 120 180

• Nothing

In Java, each child class can have only one parent.

• True

• False