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Java supports concurrency through threads which are lightweight processes. A thread is similar to a real process in that a thread and a running program are threads of execution. A thread takes advantage of the resources allocated for that program instead of having to allocate those resources again. A thread has its own stack and program counter. The code running within the thread works only within the context implied by the stack and PC, also called an execution context.

Creating Java Threads
There are two ways to create our own Thread object:

Subclassing the Thread class and instantiating a new object of that class
Implementing the Runnable interface

In both cases the run() method should be implemented. This is elaborated with the help of following examples:

Example of Extending Thread

public class ThreadExample extends Thread {
   public void run () {
      for (int i = 1; i <= 100; i++) {
         System.out.println(“Thread: ” + i);
	  }
   }
}

Example of Implementing Runnable

public class RunnableExample implements Runnable {
   public void run () {
      for (int i = 1; i <= 100; i++) {
         System.out.println (“Runnable: ” + i);
      }
   }
}

It may be noted that both of these are very similar to each other with minor syntactic and semantic differences.

Starting the Threads
A thread is started by simply sending the start message to the thread. This is shown in the following example:

public class ThreadsStartExample {
   public static void main (String argv[]) {
      new ThreadExample ().start ();
      new Thread(new RunnableExample ()).start ();
   }
}

Next >>> Lesson No. 22: Java Threads 2