Optimize memory usage of a collection of Strings in Java

Question

I have a large number of name - value pairs (approx 100k) that I need to store in some sort of cache (say a hash map) where the value is a string with an average of about 30

Answer 1

String.intern is the obvious choice as Brian says. But if you don't want to intern across all the String in memory, you can use a Set to first see if the value is present. Here's untested code. You will have to work out removing from reverse map when removing from main

  class Map2 implements Map
  {
    Map _map = Maps.newHashMap();
    Set _rev = Maps.newHashMap();

    V put(K k, V v) {
      if (_rev.containsKey(v)) {
        V prev = _rev.get(v);
        return _map.put(k, prev);
      } else {
        _rev.put(v, v);
        return _map.put(k,v);
      }
   }