Avoid Deadlock example

Question

I am wondering what are the alternative ways to avoid deadlock in the following example. The following example is a typical bank account transferring deadlock problem. What

Answer 1

This is a classic question. I see two possible solutions:

1. To sort accounts and synchronize at account which has an id lower than another one. This method mentioned in the bible of concurrency Java Concurrency in Practice in chapter 10. In this book authors use system hash code to distinguish the accounts. See java.lang.System#identityHashCode.
2. The second solution is mentioned by you - yes you can avoid nested synchronized blocks and your code will not lead to deadlock. But in that case the processing might have some problems because if you withdraw money from the first account the second account may be locked for any significant time and probably you will need to put money back to the first account. That's not good and because that nested synchronization and the lock of two accounts is better and more commonly used solution.