I just finished reading this post: What's the advantage of a Java-5 ThreadPoolExecutor over a Java-7 ForkJoinPool? and felt that the answer is not straight enough.
Can you explain in simple language and examples, what are the trade-offs between Java 7's Fork-Join framework and the older solutions?
I also read the Google's #1 hit on the topic Java Tip: When to use ForkJoinPool vs ExecutorService from javaworld.com but the article doesn't answer the title question when, it talks about api differences mostly ...
Fork-join allows you to easily execute divide and conquer jobs, which have to be implemented manually if you want to execute it in ExecutorService. In practice ExecutorService is usually used to process many independent requests (aka transaction) concurrently, and fork-join when you want to accelerate one coherent job.