Calling Object.wait while two locks are held may cause deadlock, because only one lock is released by wait.

See if one of the locks should continue to be held while waiting for a condition on the other lock. If not, release one of the locks before calling Object.wait.

In the following example of the problem, printText locks both idLock and textLock before it reads the value of text. It then calls textLock.wait, which releases the lock on textLock. However, setText needs to lock idLock but it cannot because idLock is still locked by printText. Thus, deadlock is caused.

In the following modification of the above example, id and text are included in the class Message. The method printText synchronizes on the field message before it reads the value of message.text. It then calls message.wait, which releases the lock on message. This enables setText to lock message so that it can proceed.

Java API Documentation: Object.wait().