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.
  
  Objective-C

  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(); } }

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  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:
  
  Objective-C

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

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

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

  Objective-C

  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."); } } }

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  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."); } } }