For HashMap, should I override hashCode for key or value?

Question

Does HashMap use the hashCode and equals methods of the key or value to store its entries, i.e., which is the class whose hashCode and equals methods we need to override? Should it be the key's class (K), or the value's class (V)?

Answer 1

The value is essentially irrelevant to the Map itself: it's only the key which is considered by the HashMap when it is deciding where to put the key/value pair within its internal data structure.

However, you might want to override it for the value too, e.g. if you need to do map.values().contains(...).