Question

I wrote below code to satisfy program requirement as follows:

Average of Three Write a program that reads three whole numbers and
displays the average of the three numbers.

Input Notes: Three whole numbers (non-negative integers) are entered
at the console.

Output Notes (Prompts and Labels): The program prompts for the three
integers with these strings: “Enter the first integer.”, “Enter the
second integer.”, “Enter the third integer.”. The program then prints
        The average of NUMBER1,  NUMBER2,  and NUMBER3  = AVG   where NUMBER1  is the first integer value entered and NUMBER2  and NUMBER3 
the subsequent integers, and AVG  is the computed average value.

SPECIFICATION OF NAMES: Your application class should be called
Average3:

My source code:

import java.util.Scanner;
public class Average3 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        int AVG, NUMBER1, NUMBER2, NUMBER3;
        System.out.println("Enter the first integer.");
        Scanner keyboard = new Scanner(System.in);
        NUMBER1 = keyboard.nextInt();
        System.out.println("Enter the second integer.");
        NUMBER2 = keyboard.nextInt();
        System.out.println("Enter the third integer.");
        NUMBER3 = keyboard.nextInt();
        AVG = (NUMBER1 + NUMBER2 + NUMBER3) / 3;
        System.out.println("The average of NUMBER1, NUMBER2, and NUMBER3 = " + AVG);

    }

}

My program compiles fine but I know I could have implemented and invoked an object with an associated method but am struggling where to start I understand the methods and objects conceptually but not as far as writing code. Anyone have any suggestions?

Answer 1

First, I would create a class InputData that would store the inputs from the user:

class InputData {
    public int number1;
    public int number2;
    public int number3;
}

This in itself is a useful general technique: collect several related values into a single data structure. You can then either rewrite your main method to use this class instead of three separate int variables, or you can go one step further and add some behavior to the InputData class. The obvious first behavior to add would be to compute the average:

class InputData {
    public int number1;
    public int number2;
    public int number3;

    public int average() {
        return (number1 + number2 + number3) / 3;
    }
}

With this, you could rewrite your main as follows:

public class Average3 {
    static class InputData {
        public int number1;
        public int number2;
        public int number3;

        public int average() {
            return (number1 + number2 + number3) / 3;
        }
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        InputData input = new InputData();
        System.out.println("Enter the first integer.");
        Scanner keyboard = new Scanner(System.in);
        input.number1 = keyboard.nextInt();
        System.out.println("Enter the second integer.");
        input.number2 = keyboard.nextInt();
        System.out.println("Enter the third integer.");
        input.number3 = keyboard.nextInt();
        System.out.println("The average of NUMBER1, NUMBER2, and NUMBER3 = "
            + input.average());
    }
}

Notice that I’ve made InputData a static inner class of Average3. It could also have been a separate, top-level class in the same file (as long as it wasn’t public) or a class in a separate file.

An improvement on this would be to use an array instead of separate int fields in the InputData class. Your program might then look like this:

public class Average3 {
    static class InputData {
        public int[] numbers;

        InputData(int size) {
            numbers = new int[size];
        }

        public int average() {
            int sum = 0;
            for (int number : numbers) {
                sum += number;
            }
            return sum / numbers.length;
        }
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        String[] prompts = { "first", "second", "third" };
        InputData input = new InputData(3);
        Scanner keyboard = new Scanner(System.in);
        for (int i = 0; i < prompts.length; ++i) {
            System.out.println("Enter the " + prompts[i] + " integer.");
            input.numbers[i] = keyboard.nextInt();
        }
        System.out.println("The average of NUMBER1, NUMBER2, and NUMBER3 = "
            + input.average());
    }
}

Here I’ve added a constructor to InputData to initialize the array and given it an argument to set the size of the array.

You could then introduce additional improvements like making the number of input values dynamic (using an ArrayList<Integer> instead of an int array). But this goes beyond the specific requirements of the assignment. Some people (many, actually) tend to do this kind of generalization automatically. However, advocates of Extreme Programming will point out that it is generally better to keep things simple: design and code for the needs of today instead of those of tomorrow, next week, or next month.

In other words, you don’t know what the next assignment will bring, so however you generalize beyond the immediate assignment might be wasted work.