Question

Consider the following class definition:

                  public class Parent {

              private int varA;

              protected double varB;

              public Parent(int a, double b){

varA = a;

varB = b;

              }

              public int sum( ){

                   return varA + varB;

              }

public String toString( ){

                   return "" + varA + "   " + varB;

              }

        }

Consider that you want to extend Parent to Child. Child will have a third int instance data varC.

1. Write the parameterized constructor definition for Child;
2. Write the code to override the sum() method to now add all three values and return the sum;
3. Write the code to define a method average() to calculate and return the average of varB and varC.
4. Write the code to override the toString() method for Child.

Using the class definitions for Parent and Child from Question 2, write a Java application that will represent a family of 4 members.

1. Declare a Parent array of size 4 called family.
2. Instantiate two objects of type Parent using the parameterized constructor and assign each to the first two elements of family. Use values retrieved from the user as the parameter values.
3. Instantiate two objects of type Child using the parameterized constructor and assign each to the last two elements of family. Use values retrieved from the user as the parameter values.
4. Invoke the average() method for the two Child objects and display the result.
5. Write a loop to display the member values of each object in family using the toString() method.

Answer 1

Child.java

public class Child extends Parent {

   private int varC;

   public Child(int a, double b, int c) { // parameretized construc
       super(a, b);
       varC = c;
   }

   @Override
   public int sum() { // overridden sum
       return super.sum() + varC; // returns sum of all three variables
   }

   public double average() { // average method
       return (varB + varC) / 2; // returns average
   }

   @Override
   public String toString() { // overridden toString
       return super.toString() + " " + varC;
   }

}

Application.java

import java.util.Scanner;

public class Application { // Application

   public static void main(String[] args) {

       Scanner input = new Scanner(System.in);
      
       Parent p1 = getParentfromUser(input, 1);
       Parent p2 = getParentfromUser(input, 2);
       Child c1 = getChildfromUser(input, 1);
       Child c2 = getChildfromUser(input, 2);
      
       Parent[] family = {p1, p2, c1, c2};
      
       System.out.println("average of child " + 1 + " " + c1.average());
       System.out.println("average of child " + 2 + " " + c2.average());
      
       for(Parent p : family) {
           System.out.println(p);
       }

   }

   static Parent getParentfromUser(Scanner input, int id) {
       Parent parent;
       System.out.println("input varA for parent " + id);
       int a = input.nextInt();
       System.out.println("input varB for parent " + id);
       double b = input.nextDouble();
       parent = new Parent(a, b);
       return parent;
   }

   static Child getChildfromUser(Scanner input, int id) {
       Child child;
       System.out.println("input varA for child " + id);
       int a = input.nextInt();
       System.out.println("input varB for child " + id);
       double b = input.nextDouble();
       System.out.println("input varC for child " + id);
       int c = input.nextInt();
       child = new Child(a, b, c);
       return child;
   }

}

Output:

input varA for parent 1
1
input varB for parent 1
2
input varA for parent 2
3
input varB for parent 2
4
input varA for child 1
2
input varB for child 1
1
input varC for child 1
3
input varA for child 2
5
input varB for child 2
5
input varC for child 2
5
average of child 1 2.0
average of child 2 5.0
1 2.0
3 4.0
2 1.0 3
5 5.0 5