[layer8]

To add to this: Java’s original collection classes (Vector, Hashtable, …) were thread-safe, but it turned out that the performance penalty for that was too high, all the while still not catching errors when performing combinations of operations that need to be a single atomic transaction. This was one of the motivations for the thread-unsafe classes of the newer collection framework (ArrayList, HashMap, …).

[wging]

> still not catching errors when performing combinations of operations that need to be a single atomic transaction

This is so important. The idea that code is thread-safe just because it uses a thread-safe data structure, and its cousin "This is thread-safe, because I have made all these methods synchronized" are... not frequent, but I've seen them expressed more often than I'd like, which is zero times.

[magicalhippo]

Shows up in other places as well, such as file systems. Trying to check if a filename exists, and if it doesn't then create the file for example. Instead one should simply try to create the file and handle the error if it already exists.