How to piece of occupation Multiple Threads inwards Java - Example

In gild to usage multiple threads inwards Java, y'all demand to kickoff define the labor which volition last executed past times those threads. In gild to create those task, y'all tin either usage Runnable or Callable interface. If y'all are simply learning Java chose Runnable, it's simpler one, but if y'all are familiar amongst Java multithreading together with desire to leverage additional features offered past times Callable e.g. it tin throw an exception together with it tin also furnish value, together with hence acquire ahead together with usage Callable. Once y'all receive got labor ready, y'all demand to create an event of Thread class. You tin create equally many instances equally y'all want, but beware don't create equally good many Thread instances inwards Java because both JVM together with Operating organization has a boundary on how many threads y'all tin create inwards Java. Crossing that boundary volition resultant inwards java.lang.OutOfmemoryError: could non create a native thread. For the usage of this example, creating simply 3 threads are enough.

Let's assume nosotros create threads T1, T2, together with T3. While creating nosotros exceed them an event of your Task class, which extends Runnable. Always remember, y'all cannot exceed an event of whatsoever arbitrary class, y'all must exceed either Callable or Runnable. Any code which is written inwards the run() or call() will together with hence last executed past times the thread y'all passed your labor to.

You tin read Core Java Volume 1 - Fundamentals past times Cay S. Horstmann together with Effective Java past times Joshua Bloch to larn to a greater extent than near how to attain effective multithreading

How to start a Thread inwards Java

Just creating an event of Thread doesn't start them, y'all demand to start each thread manually past times calling Thread.start() method. This method kickoff creates a thread together with and hence telephone telephone run() method of Runnable labor y'all passed to it inwards this novel thread.

If y'all straight telephone telephone run() method together with hence the code volition last executed inwards the same thread on which y'all called run() method, multi-threading or concurrency volition non last achieved.

This is also i of the mutual mistakes many Java developers make, y'all tin read to a greater extent than near it here.

As I said, y'all farther read Core Java Volume 1 - Fundamentals past times Cay S. Horstmann to larn to a greater extent than near Threads inwards Java. It also covers advanced multi-threading concepts e.g. using concurrency utilities similar CountDownLatch, CyclicBarrier or Phaser inwards Java application.

In gild to usage multiple threads inwards Java How to usage Multiple Threads inwards Java - Example

Java Program to Create together with Run a Thread

Here is a Java Program to demonstrate how to usage thread past times kickoff creating an event of java.lang.Thread flat together with subsequently past times calling the start method.

/**  * Simple Java programme to demonstrate how to usage multiple threads.  * Steps to usage  * multiple threads inwards Java :   * 1. Implement Runnable interface to position the code  * y'all desire to run inwards split thread.   * 2. Create an Instance of Thread flat past times  * passing an event of Runnable y'all simply created.   * 3. Call Thread.start()  * method, this volition execute the code inwards split thread.  *   * @author WINDOWS 8  *  */ public class MultipleThreadDemo {      private static class ParallelTask implements Runnable {          @Override         public void run() {             System.out.println(Thread.currentThread().getName()                     + " is executing this code");          }      }      public static void main(String[] args) {          // created 3 threads but none volition start until y'all call         // start() method         Thread t1 = new Thread(new ParallelTask(), "Thread - T1");         Thread t2 = new Thread(new ParallelTask(), "Thread - T2");         Thread t3 = new Thread(new ParallelTask(), "Thread - T3");          // now, let's start all 3 threads         t1.start();         t2.start();         t3.start();     }  }   Output Thread - T1 is executing this code Thread - T3 is executing this code Thread - T2 is executing this code

Once a Thread finishes the terminal describe of piece of occupation of code within run() method, or it came out of run() method past times using furnish disputation or it came out of run() due to an exception is thrown, the thread is finished. You tin non reuse this thread again. Calling the start() method on such thread volition resultant inwards IllegalThreadStateException.

Here is a squeamish diagram which explains the lifecyle of a thread inwards Java:

Also, when y'all start multiple threads at the same fourth dimension inwards Java, in that place is no guarantee that which thread volition start execution first. It is possible that T3 starts processing earlier T1 fifty-fifty when y'all telephone telephone start() method on T1 first. This is the chore of Thread scheduler.

Further Learning
Java Fundamentals Part 1,2
Java Concurrency inwards Practice
Applying Concurrency together with Multi-threading to Common Java Patterns