Is a HashMap a proper data structure

Question

I store in a HashMap 3 types of object.

HashMap>

[\'Lorry\', [list of lorries]]
[\'Sport\', [list of sport\'s cars]]
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Answer 1

The basic approach is sound, however since you only want to store each instance once, a Set is a better choice than a List for the map entry value:

Map> typeCache = new HashMap>();

The contains() method of HashSet is very fast indeed, so finding if your map contains a particular instance in it values is not going to cost much.

Using two maps would probably be better though - once for each type of lookup, so also use:

Map idCache = new HashMap();