Unit 9 topic 2 quiz

public class ClassA

{  public void method1()

{ /* implementation of method1 / }

} public class ClassB extends ClassA {

public void method1(){

/ implementation of method1 / }

public void method2(){

/ implementation of method2 */ }

}

Which of the following is method1() in ClassB an example of?

• information hiding

• polymorphism

• procedural abstraction

• method overriding

• method overloading

Answer explanation

Method overriding occurs whenever a method in a superclass is redefined in a subclass. Method overloading occurs when methods in the same class have the same name but different parameter types. In polymorphism, the correct overridden method is called for a particular subclass object during run time. Information hiding is the use of private to restrict access. Procedural abstraction is the use of helper methods.

class Cars {

void TransmissionType() {

System.out.println("Manual Transmission"); } }

class ElectricCar extends Cars

{ void TransmissionType()

{ System.out.println("AMT Transmission"); }

void showInfo() {

this.TransmissionType(); super.TransmissionType(); }

}

public class MethodOverridingCar {

public static void main(String[] args) {

ElectricCar ec = new ElectricCar(); ec.showInfo(); }

}

What will be the output of this code segment with method overriding and the keyword super?

• Manual Transmission

  AMT Transmission

• AMT Transmission

  Manual Transmission

• AMT Transmission

  AMT Transmission

• no output

• Manual Transmission

  Manual Transmission

Answer explanation

The this keyword calls the subclass overridden method. The super keyword calls the method of the superclass. So, the output will display the subclass method and then the superclass method, as follows:

AMT Transmission

Manual Transmission

Which of the following classes is the superclass of every class in Java?

• Abstract class

• ArrayList class

• String class

• Math class

• Object class

Answer explanation

The Object class is the superclass of every class in Java. It is stored in the java.lang package and is the ultimate superclass of all Java classes except for the Object class itself.

Also, arrays extend the Object class. However, interfaces do not extend the Object class.

class Superclass{

/* instance variable / 

int a = 10;  / static variable */  static int b = 20; }

class Subclass extends Superclass{

void assignment(){

System.out.println(super.a);

System.out.println(super.b); }

public static void main(String[] args) {     

Subclass mo = new Subclass(); super.a = 700; mo.assignment(); } }

What will be the output of this code segment?

• 700

  20

• no output

• compilation error

• 10

  20

• run time error

Answer explanation

You cannot use the super keyword with a static variable; therefore, it will give a compilation error.

class Superclass{

/* instance variable / 

int a = 36;

/ static variable */ 

static double x = 12.2; }

class Subclass extends Superclass{ void display() { super.a = 1;

System.out.println(a); super.x = 60.3;

System.out.println(x); }

public static void main(String[] args) {     

Subclass m = new Subclass();    

 m.display(); } }

 What will be the output of this code segment?

• 1

  1

• no output

• compilation error

• run time error

• 1

  60.3

Answer explanation

The display() method is referring the class Parent instance variable (that is, a) super.a = 1; and then referring to the class Parent static variable (that is, x), assigning a new value super.x = 60.3;. The super keyword can access the static variables in the subclass. Therefore, it will display the following:

1

60.3

The keyword, this, is used to refer to the current class instance variables.

• True

• False

The keyword, this, can be passed as an argument in the method call representing the current object of the class.

• True

• False

The keyword, this, can be used to invoke only the subclass class methods.

• True

• False

The keyword, this, is used to initiate a constructor of the current class.

• True

• False

The keyword, this, cannot be used to access the static variables of the current instance.

• True

• False