Synchronized blocks vs methods.

[Paul Roubekas]

In the following code synchronized is used in a way I do not understand. What is "synchronized" the Objects "lock1" and "lock2" or the code inside the {}?

<font size=2.5>
public class TestClass extends Thread 
{
   static Object lock1 = new Object();
   static Object lock2 = new Object();
   static volatile int i1, i2, j1, j2, k1, k2;
   public void run() 
   {             
      while (true) 
      {
         workWithLocks();
         workWithoutLocks();     
      } 
   } 
   void workWithLocks() 
   {
      synchronized(lock1) { i1++ ;  i2++; }
      synchronized(lock2) { k1++ ; k2++ ; }
      j1++;    j2++;
   }
   void workWithoutLocks() 
   {
      if (i1 != i2) System.out.println("i");
      if (j1 != j2) System.out.println("j"); 
      if (k1 != k2) System.out.println("k");
   }
   public static void main(String args[]) 
   {
      new TestClass().start();
      new TestClass().start();
   }
}

[This message has been edited by Cindy Glass (edited September 25, 2001).]

[Anonymous]

The code inside the {} is "synchronized" using the locks on two arbitrary objects "lock1" and "lock2". The objects are not synchronized.
In most cases that you've probably seen the lock being used is implicit -- it is the object's who owns the synchronized method.
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Sun Certified Programmer for the Java� 2 Platform

[Bill Hause]

The code inside the {} is what is synchronized.
No thread can execute the code in the {} unless it has the "one and only" lock on the "mutex" objects "lock1" or "lock2".
lock1 and lock2 simply serve as objects to lock onto. Note they are static so there is only one instance of each across all instances of TestClass.
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[Paul Roubekas]

That's right, duh! you can only synch. on one class at a time even if more then one method is synch'ed in the class. So all synch'ed blocks of code must piggieback onto some class.
That clears it up for me, thanks a bunch!