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/*
* 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();
}
}
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