Java API contains numerous Collection and Map implementations so it might be confusing to figure out which one to use. Here is a quick flowchart that might help with choosing from the most common implementations.
This cheat sheet doesn't include rarely used classes like
LinkedList, etc. because they are designed for very specific or exotic tasks and shouldn't be chosen in 99% cases.
If you are interested in other built-in collection implementations, Alexander Zagniotov provided a detailed flowchart for many more collections in his article.