Introducing Extensions - Design Patterns Java - page 215

You may have noticed that the pop() method of BinStack calls notify() before it pops
an object from the stack. If a waiting thread were to wake up and start accessing the stack
before this method pops an object, the stack would overflow.
CHALLENGE 26.2
There is, in fact, no danger in the BinStack code that a thread waiting to push an
object will start executing before the pop() method completes its pop. Why is that?
The Object class comments provide a surprising amount of documentation on how wait()
and notify() work. Another excellent reference on these methods is The Java™ Class
Libraries, Volume 1 (Chan, Lee, and Kramer 1998). For an extensive work on many
applications of Java's locking facilities, I also recommend Concurrent Programming in
Java™ (Lea 2000).
To use a BinStack object, create a thread that pushes or pops an object to the stack.
The actionPerformed() method of ShowWaitAndNotify provides an example:
public void actionPerformed(ActionEvent e)
{
Object source = e.getSource();
if (source.equals(loadButton()))
{
new Thread()
{
public void run()
{
loadButton().setEnabled(false);
binStack().push(new Bin("a bin"));
loadButton().setEnabled(true);
stackPanel().repaint();
}
}
.start();
}
if (source.equals(unloadButton()))
{
new Thread()
{
public void run()
{
unloadButton().setEnabled(false);
binStack().pop();
unloadButton().setEnabled(true);
stackPanel().repaint();
}
}
.start();
}
}