Errata

Assuming Two Threads invoke newCharacter(),may be some error！

"The character-reading thread still executes the sleep() method, which won't be interrupted (since the main thread has already completed the interrupt() method)".

This is impossible. After interrupt() method finish, the character-reading thread throws InterruptedException in the sleep() method call.

Please, see the InterruptedException in javadoc's Thread.sleep().

2nd paragraph of p65 says, "in the same order as the newCharacter".
However, the order for getting the locks is not correct.

public void newCharacter(CharacterEvent ce){
try {
scoreLock.lock();
charLock.lock();
}
...
...
finally {
scoreLock.unlock();
charLock.unlock();
}
}

should be replaced by

public void newCharacter(CharacterEvent ce){
try {
scoreLock.lock();
charLock.lock();
}
...
...
finally {
charLock.unlock();
scoreLock.unlock();
}
}

---------------------------------------------------------------
Author's comments: The lock() method calls are all done in the
beginning of the method. And the lock() method does not throw any
exceptions. Hence, it is not necessary to check to see if the lock is
already grabbed before unlocking it. In the finally clause, it is
guaranteed that both locks are grabbed, and need to be released.

The finally clause's purpose is to release both locks -- locks that
are guaranteed to be owned. And it is only releasing those two locks.
While it is "prettier" to release the locks in the reverse order in
which they are grabbed, it is not necessary in this case.
---------------------------------------------------------------

Prior to Java 1.5, the double-checked locking idiom in Java was broken as the author indicated in this paragraph.

However, as I understood it the changes to the memory model and particularly to the sematics of volatile in Java 1.5 now allow the use of this idiom, providing that the lazily initialized object is a volatile field.

I include links to articles I have recently seen regarding this for further explanation:
http://www.ibm.com/developerworks/library/j-jtp03304/
http://www.cs.umd.edu/~pugh/java/memoryModel/jsr-133-faq.html#volatile

The paragraph on double-checked locking should be changed to reflect this change in Java 1.5.