Java Semaphore - Print even and odd numbers using Threads

In previous chapter we saw what are semaphores and how to use them. In this chapter we will be implementing a program to print even and odd numbers using semaphore. We will be creating a semaphore with single permit. This semaphore will be shared by 2 threads. One thread will print even numbers and the other will print odd numbers.

Semaphore - Table Of Contents
Understanding Java Semaphore
Java Semaphore - Print even and odd numbers using Threads
Java Semaphore - Print numbers sequence using three Threads

•           Step 1                           Step2

     

•           Step 3                           Step4

        

package com.javastructures;
import java.util.concurrent.Semaphore;

public class SemaphoreExample {

	public static void main(String[] args) {

        //We dont want the even number printed first so the initial permit for this semaphore is 0.
		Semaphore evenSemaphore = new Semaphore(0);
		//We want to print the odd number first so the initial permit for this semaphore is 1.
		Semaphore oddSemaphore = new Semaphore(1);
		
		PrintOddNumber printOddNumber = new PrintOddNumber(evenSemaphore, oddSemaphore);
		PrintEvenNumber printEvenNumber = new PrintEvenNumber(evenSemaphore, oddSemaphore);
		
		new Thread(printOddNumber, "Print Odd").start();
		new Thread(printEvenNumber, "Print Odd").start();
	}

}

class PrintEvenNumber implements Runnable {

	Semaphore sempahoreEven;
	Semaphore sempahoreOdd;

	public PrintEvenNumber(Semaphore sempahoreEven, Semaphore sempahoreOdd) {
		super();
		this.sempahoreEven = sempahoreEven;
		this.sempahoreOdd = sempahoreOdd;
	}

	@Override
	public void run() {
		for (int i = 2;; i = i + 2) {
			try {
			    //This will decrement the permit used by the even semaphore to 0. 
				sempahoreEven.acquire();
				System.out.println(i);
				//This will increment the permit used by odd semaphore by 1.
				sempahoreOdd.release();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

}

class PrintOddNumber implements Runnable {

	Semaphore sempahoreEven;
	Semaphore sempahoreOdd;

	public PrintOddNumber(Semaphore sempahoreEven, Semaphore sempahoreOdd) {
		this.sempahoreEven = sempahoreEven;
		this.sempahoreOdd = sempahoreOdd;
	}

	@Override
	public void run() {
		for (int i = 1;; i = i + 2) {
			try {
			    //This will decrement the permit used by the odd semaphore to 0. 
				sempahoreOdd.acquire();

				Thread.sleep(1000);
				System.out.println(i);
				//This will increment the permit used by even semaphore by 1.
				sempahoreEven.release();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}

		}

	}

}

Run the program as a Java Application -