ThreadDemo.java Source code

Introduction

Here is the source code for ThreadDemo.java

Source

/*
 * Copyright (c) 2004 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 3nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose,
 * including teaching and use in open-source projects.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book, 
 * please visit http://www.davidflanagan.com/javaexamples3.
 */

/**
 * This class demonstrates the use of threads. The main() method is the initial
 * method invoked by the interpreter. It defines and starts two more threads and
 * the three threads run at the same time. Note that this class extends Thread
 * and overrides its run() method. That method provides the body of one of the
 * threads started by the main() method
 */
public class ThreadDemo extends Thread {
    /**
     * This method overrides the run() method of Thread. It provides the body for
     * this thread.
     */
    public void run() {
        for (int i = 0; i < 5; i++)
            compute();
    }

    /**
     * This main method creates and starts two threads in addition to the initial
     * thread that the interpreter creates to invoke the main() method.
     */
    public static void main(String[] args) {
        // Create the first thread: an instance of this class. Its body is
        // the run() method above
        ThreadDemo thread1 = new ThreadDemo();

        // Create the second thread by passing a Runnable object to the
        // Thread() construtor. The body of this thread is the run() method
        // of the anonymous Runnable object below.
        Thread thread2 = new Thread(new Runnable() {
            public void run() {
                for (int i = 0; i < 5; i++)
                    compute();
            }
        });

        // Set the priorities of these two threads, if any are specified
        if (args.length >= 1)
            thread1.setPriority(Integer.parseInt(args[0]));
        if (args.length >= 2)
            thread2.setPriority(Integer.parseInt(args[1]));

        // Start the two threads running
        thread1.start();
        thread2.start();

        // This main() method is run by the initial thread created by the
        // Java interpreter. Now that thread does some stuff, too.
        for (int i = 0; i < 5; i++)
            compute();

        // We could wait for the threads to stop running with these lines
        // But they aren't necessary here, so we don't bother.
        // try {
        // thread1.join();
        // thread2.join();
        // } catch (InterruptedException e) {}

        // The Java VM exits only when the main() method returns, and when all
        // threads stop running (except for daemon threads--see setDaemon()).
    }

    // ThreadLocal objects respresent a value accessed with get() and set().
    // But they maintain a different value for each thread. This object keeps
    // track of how many times each thread has called compute().
    static ThreadLocal numcalls = new ThreadLocal();

    /** This is the dummy method our threads all call */
    static synchronized void compute() {
        // Figure out how many times we've been called by the current thread
        Integer n = (Integer) numcalls.get();
        if (n == null)
            n = new Integer(1);
        else
            n = new Integer(n.intValue() + 1);
        numcalls.set(n);

        // Display the name of the thread, and the number of times called
        System.out.println(Thread.currentThread().getName() + ": " + n);

        // Do a long computation, simulating a "compute-bound" thread
        for (int i = 0, j = 0; i < 1000000; i++)
            j += i;

        // Alternatively, we can simulate a thread subject to network or I/O
        // delays by causing it to sleep for a random amount of time:
        try {
            // Stop running for a random number of milliseconds
            Thread.sleep((int) (Math.random() * 100 + 1));
        } catch (InterruptedException e) {
        }

        // Each thread politely offers the other threads a chance to run.
        // This is important so that a compute-bound thread does not "starve"
        // other threads of equal priority.
        Thread.yield();
    }
}