code: public V get (K key)
      {
          V value = null;
          SoftReference<V> ref = _map.get(key);
          if (ref != null) {
              value = ref.get();
              if (value == null) {
                  _map.remove(key);
              }
          }
          return value;
      }
docs: Looks up and returns the value associated with the supplied key.