How to select a random key from a HashMap in Java?

Question

I\'m working with a large ArrayList>, and I would repeatedly need to select a random key from a random HashMap (and do some stuff with it).

Answer 1

I'm assuming you are using HashMap as you need to look something up at a later date?

If not the case, then just change your HashMap to an Array/ArrayList.

If this is the case, why not store your objects in a Map AND an ArrayList so you can look up randomly or by key.

Alternatively, could you use a TreeMap instead of HashMap? I don't know what type your key is but you use TreeMap.floorKey() in conjunction with some key randomizer.