Java Hashmap: How to get key from value?

Question

If I have the value \"foo\", and a HashMap ftw for which ftw.containsValue(\"foo\") returns true, how can I

Answer 1

You could insert both the key,value pair and its inverse into your map structure

map.put("theKey", "theValue");
map.put("theValue", "theKey");

Using map.get("theValue") will then return "theKey".

It's a quick and dirty way that I've made constant maps, which will only work for a select few datasets:

• Contains only 1 to 1 pairs
• Set of values is disjoint from the set of keys (1->2, 2->3 breaks it)