Listing Odd Numbers in Java

What are Odd Numbers?

Odd numbers are numbers that are not divisible by 2.

They include:

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, ...

Thankfully, odd numbers complement even numbers. So our Java code for listing odd numbers is almost same as the one for even numbers.

Create a new class file; File, New File.
Call it OddNumbers.
Type out the adjoining Java code for listing odd numbers.

Note: You can comment out the evenNumbers Java object code in the main class from the previous lesson or simply continue from where it stopped.

Code for Odd Number List with Input in Java

For a little more flexibility, let's add an input form.

All we need is a way to ask the user for input.
For this purpose, we'll import and use the System.in and Scanner library classes.

Java code for OddNumbers class .

package arithmetic;

public class OddNumbers {

    private int start; // Our starting point
    private final int stop; // where we will stop
    private String result; // Store result here.

    OddNumbers(int first, int last) {
        start = first;
        stop = last;
        result = "Odd numbers between " + first + " and " + last + " are: \n";
    }

    String prepResult() {
        /*
        * Loop from start to stop and rip out odd numbers;
         */
        while (start <= stop) {
            if (start % 2 != 0) {
                result += start + "; "; // Mind the '+' in front of the '='
            }
            start++; // increase start by 1(same as start = start + 1
        }
        return result;
    }

}

Main class.

package arithmetic;

public class Arithmetic {

    public static void main(String[] args) {
        System.out.println("Welcome to our demonstration sequels");
        System.out.println("Hope you enjoy (and follow) the lessons.");
        System.out.println("");

        /* Use the Odd Number class. */
        OddNumbers odd_data = new OddNumbers(1, 100); // odd numbers between 1 and 100
        System.out.println(odd_data.prepResult());

        System.out.println();
    }

}

Main class for Collecting Input.

package arithmetic;

import java.util.Scanner;

public class Arithmetic {

    public static void main(String[] args) {
        System.out.println("Welcome to our demonstration sequels");
        System.out.println("Hope you enjoy (and follow) the lessons.");
        System.out.println("");

        /*
        * Collect input.
         */
        int first;
        int last;
        String collect_input; // For collecting user input

        /* Scanner takes care of collecting input using the System.in object. */
        Scanner user_choice = new Scanner(System.in);

        System.out.print("Enter your start number:   ");
        collect_input = user_choice.next(); // user input is a String object
        first = Integer.parseInt(collect_input); // Convert it to integer

        System.out.print("Enter your stop number:   ");
        collect_input = user_choice.next();
        last = Integer.parseInt(collect_input);

        // Use the Odd Number class.
        OddNumbers odd_input = new OddNumbers(first, last);
        System.out.println(odd_input.prepResult());

        System.out.println();
    }

}

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