如何在不知道需要多少个 ArrayList 的情况下创建一个 Map 的 ArrayList？

Question

The way my program works is it gets an arraylist of some object "World". I want to create a new arraylist for every World. I then want to create a map where the name of a World is the key, and a arraylist is the value. So far, I can get an unique id for each World and the size of the arraylist of Worlds, but I don't know how to create that map.

Answer 1

You can use any of the classes that implement the Map interface, eg HashMap:

Map<String, ArrayList<World>> map = new HashMap<String, ArrayList<World>>();