Java/Threads/Volatile

Illustrate the volatile variables

   <source lang="java">

public class Volatile extends Object implements Runnable {

 // not marked as "volatile", but it should be!
 private int value;
 private volatile boolean missedIt;
 // doesn"t need to be volatile-doesn"t change
 private long creationTime;
 public Volatile() {
   value = 10;
   missedIt = false;
   creationTime = System.currentTimeMillis();
 }
 public void run() {
   print("entering run()");
   // each time, check to see if "value" is different
   while (value < 20) {
     // Used to break out of the loop if change to
     // value is missed.
     if (missedIt) {
       int currValue = value;
       // Simply execute a synchronized statement on an
       // arbitrary object to see the effect.
       Object lock = new Object();
       synchronized (lock) {
         // do nothing!
       }
       int valueAfterSync = value;
       print("in run() - see value=" + currValue
           + ", but rumor has it that it changed!");
       print("in run() - valueAfterSync=" + valueAfterSync);
       break;
     }
   }
   print("leaving run()");
 }
 public void workMethod() throws InterruptedException {
   print("entering workMethod()");
   print("about to sleep for 2 seconds");
   Thread.sleep(2000);
   value = 50;
   print("just set value=" + value);
   print("about to sleep for 5 seconds");
   Thread.sleep(5000);
   missedIt = true;
   print("just set missedIt=" + missedIt);
   print("about to sleep for 3 seconds");
   Thread.sleep(3000);
   print("leaving workMethod()");
 }
 private void print(String msg) {
   long interval = System.currentTimeMillis() - creationTime;
   String tmpStr = (interval / 1000.0) + "000";
   int pos = tmpStr.indexOf(".");
   String secStr = tmpStr.substring(pos - 2, pos + 4);
   String nameStr = Thread.currentThread().getName();
   nameStr = nameStr.substring(nameStr.length() - 8, nameStr.length());
   System.out.println(secStr + " " + nameStr + ": " + msg);
 }
 public static void main(String[] args) {
   try {
     Volatile vol = new Volatile();
     // slight pause to let some time elapse
     Thread.sleep(100);
     Thread t = new Thread(vol);
     t.start();
     // slight pause to allow run() to go first
     Thread.sleep(100);
     vol.workMethod();
   } catch (InterruptedException x) {
     System.err.println("one of the sleeps was interrupted");
   }
 }

}

      </source>