While XP works with any language, we believe it works well with Java for a few reasons. Most important is the speed with which Java compiles. XP relies on test-first development in which programmers write tests for code before they write the code. For each new feature, you should write a test and then watch the test run and fail. You should then add the feature, compile, and watch the test run successfully. This implies that you must write a little code, compile, and run the tests frequently, perhaps dozens of times each day. Because Java compiles quickly, it is well suited to the test-first approach.
-- Java Extreme Programming Cookbook (emphasis added)
This is a joke, right?