JAVA EE: Java Tutorial: Java Threads (SimpleThreads)

Friday 16 December 2016

Java Tutorial: Java Threads (SimpleThreads)

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https://www.youtube.com/watch?v=2pKSE0LMpOw&list=UUhwKlOVR041tngjerWxVccw

SimpleThreads.java

/*
 * SimpleThreads consists of two threads. The first is
 * the main thread that every Java application has. The
 * main thread creates a new thread from the Runnable
 * object, MessageLoop, and waits for it to finish. If
 * the MessageLoop thread takes too long to finish, the
 * main thread interrupts it.
 * 
 * The MessageLoop thread prints out a series of
 * messages. If interrupted before it has printed all
 * its messages, the MessageLoop thread prints a message
 * and exits.
 */

public class SimpleThreads
{

    /*
     * Display a message, preceded by the name of the
     * current thread
     */
    static void threadMessage(String message)
    {
        String threadName = Thread.currentThread().getName();
        System.out.format("%s: %s%n", threadName, message);
    }

    private static class MessageLoop implements Runnable
    {
        public void run()
        {
            String importantInfo[] =
            { "Peter goes to Japan", "Hello welcome to india",
                    "Twinkle Twinkle little star", "John is a super man" };
            try
            {
                for (int i = 0; i < importantInfo.length; i++)
                {
                    // Pause for 4 seconds
                    Thread.sleep(4000);
                    // Print a message
                    threadMessage(importantInfo[i]);
                }
            }
            catch (InterruptedException e)
            {
                threadMessage("I wasn't done!");
            }
        }
    }

    public static void main(String args[]) throws InterruptedException
    {

        // Delay, in milliseconds before
        // we interrupt MessageLoop
        // thread (default one hour).
        long patience = 1000 * 60 * 60;

        // If command line argument
        // present, gives patience
        // in seconds.
        if (args.length > 0)
        {
            try
            {
                patience = Long.parseLong(args[0]) * 1000;
            }
            catch (NumberFormatException e)
            {
                System.err.println("Argument must be an integer.");
                System.exit(1);
            }
        }

        threadMessage("Starting MessageLoop thread");
        long startTime = System.currentTimeMillis();
        Thread t = new Thread(new MessageLoop());
        t.start();

        threadMessage("Waiting for MessageLoop thread to finish");
        /*
         * loop until MessageLoop thread exits
         */
        while (t.isAlive())
        {
            threadMessage("Still waiting...");
            /*
             * Wait maximum of 1 second for MessageLoop
             * thread to finish.
             */
            t.join(1000);
            if (((System.currentTimeMillis() - startTime) > patience)
                    && t.isAlive())
            {
                threadMessage("Tired of waiting!");
                t.interrupt();
                // Shouldn't be long now
                // -- wait indefinitely
                t.join();
            }
        }
        threadMessage("Finally!");
    }
}

Output

main: Starting MessageLoop thread
main: Waiting for MessageLoop thread to finish
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
Thread-0: Peter goes to Japan
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
Thread-0: Hello welcome to india
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
Thread-0: Twinkle Twinkle little star
main: Still waiting...
main: Still waiting...
main: Still waiting...
Thread-0: John is a super man
main: Finally!