Threads - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 268

Figure 8.5 (a) The Filler and Getter threads need to access the bin in the Box .
The Getter needs, however, to wait till the bin is filled. (b) While the Filler places a
value in the bin via the synchronized put() method, the Getter cannot invoke the
synchronized get() method. (c) Similarly, the Filler must wait till the Getter
finishes invoking the get() method before it can invoke put() .
In the following code for the Box class, we see that the get() and put()
methods are prefaced by the modifier synchronized . This indicates that only
one thread can invoke either of these methods at the same time for the same object.
That is, during the time that a thread executes, say, the get() method, no other
thread can execute either the get() or put() method for the same Box object.
public class Box
{
private int fBin;
private boolean fFilled = false;
Outputable fOutput;
/** Constructor obtains reference to Outputable object.
**/
Box (Outputable out) {
fOutput = out;