Threads in Java – Part I

Overview of Threads

Software applications are single / multi threaded. A traditional or heavyweight process has a single thread of control. A process with multiple threads of control can perform more tasks at a time. Modern software packages are multi threaded. Such as a browser might have one thread to display text or images while other thread retrieves update data from the network. In certain situation, a single application required to perform similar task at a same time. The benefits of using multi threads are :

• Responsiveness : A program remain responsive even another thread is blocked or performing a larger task
• Resource Sharing : By default threads shares data and resources of the process in which they belong
• Economy : Threads are more economical in terms of creating process and memory allocation
• Scalability : The benefits of multi threading can be greatly increased in a multiprocessor architecture, where threads may be running in parallel on different processors.

In this tutorial, i will focus on java threads and how to program a multi threaded software application.

Java Threads

Java Threads API provides a rich set of features for creating and managing threads. Threads are fundamental model of program execution in a java program. All java programs comprise at least a single thread that begins execution in the program’s main() method.

Creating Threads in Java

There are two possible way to create threads in a java program.

• Create a new class that is derived from java Thread class and override its run method. The following class is derived from java Thread class and overrides its run method.

  package threads;
  /* ThreadEx1.java: A simple program creating and invoking a thread object by
   extending the standard Thread class. */
   class MyThread extends Thread {
  	public void run() {
  		System.out.println(" this thread is running ... ");
  	}
  }
  
  public class ThreadEx1 {
  	public static void main(String[] args) {
  		MyThread t = new MyThread();
  		t.start();
  	}
  }

• Define a class that implements a Runnable interface and define run method. Runnable interface is defined as follows:

  public interface Runnable
  {
  public abstract void run();
  }

  Example code for implementign Runnable interface. The following example implements Runnable interface and defines run method.

  package threads;
  
  public class RunnableController {
  	public static void main(String[] args) {
  		Task task1 = new Task();
  		task1.kickStart();
  		Thread.yield();
  		task1.terminate();
  	}
  }
  
  class Task implements Runnable {
  	private Thread thread;
  
  	public void kickStart() {
  		if (thread == null) {
  			thread = new Thread(this);
  			thread.start();
  		}
  	}
  
  	public void terminate() {
  		thread = null;
  	}
  
  	public void run() {
  		while (thread == Thread.currentThread()) {
  			System.out.println("Going around in loops.");
  		}
  	}
  }