Thread confusion - synchronized keyword

Question

Hi All,
I am trying to understand when and how to use synchronized. From my tinkering I have come to a situation that is confusing me:
I have an object with two (unsynchronized) methods (called inc and dec). These methods increment and decrement an Integer field called counter. The methods then sleep for a random amount of time.
The contents of the methods are enclosed with a synchronized block, synchronized to the field 'counter'.
I now create two threads, one calling inc the other dec continuously.
From the output the methods are not synchronizing at all.
If I change the synchronized block to sync to a different variable, eg. 'this' or an arbitrary unused object, the code synchronizes properly.
My question/problem is why does the code not synchronize properly on an object that I am altering in the synchronized block.
A second and (hopfully) related question - is:
synchronized public void foo() {...}syntactic sugar for:
public void foo() {
   synchronized (this) {...}
}Thank you for your time in reading this, any help would be very appreciated.
Alex.

Answer 1

Peter-Lawrey - Thankyou!!!
It's obvious now - by creating a new Integer object I am synchronizing on different objects in the two methods, hence still failing to lock the other thread out... DOH!
Here's one of the methods for completeness
     public void inc() {
          synchronized (this) {
               System.out.print("Inc = ");
               try {
                    sleep(1001);
               } catch (InterruptedException e) {
                    e.printStackTrace();
               counter = new Integer(counter.intValue() + 1);
               System.out.println(counter.toString());
     } As Integers are readonly I have to intValue, then increment then create a new Integer Object.
Out of curiosity - does the synchronized block fail at this point or does is now apply to the new object until the end of the block is reached?
Thankyou again for your help and returning a small part of my sanity!
Alex.