In this caching code that I worked on due to a performance problem, I got some feedback proposing to take out a bunch of the synchronized blocks because of some ignorant reasoning that the synchronized blocks don't do anything except hurt performance. My response pointed out why each of the synchronized blocks was necessary, and, for one instance, quoting the javadoc for java.util.HashMap that says, "If multiple threads access a hash map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally."

For the synchronized HashMap access, I suppose using java.util.concurrent.ConcurrentHashMap would allow the removal of the synchronization. Since ConcurrentHashMap was introduced in Java 1.5, and the code still had to be Java 1.4, I didn't mention it in my response.

I don't know what will come of this. I don't know the person making the proposal, but I suspect that it is someone who is relatively junior. I hope he or she will learn from this.