Another topic that comes up again and again in questions that people ask me is, "How does immutability work in Java"? Immutability is a godsend for concurrent programmers, because you don't have to do lots of sticky reasoning about what threads are updating what variables when, and you don't have to worry about cache thrashing, and you don't have to worry about all sorts of things. When I write concurrent code (which is reasonably often), I try to make as many things immutable as possible. Now, in common parlance, immutability means "does not change". Immutability doesn't mean "does not change" in Java. It means "is transitively reachable from a final field, has not changed since the final field was set, and a reference to the object containing the final field did not escape the constructor". In circumstances other than this, even if a given field is not mutated, the Java memory model requires that there be some form of synchr...
Jeremy Manson's blog, which goes into great detail either about concurrency in Java, or anything else that the author happens to feel is interesting or relevant to the target audience.