code: public V put(final int keyPartA, final int keyPartB, final V value) {
          final long key = compoundKey(keyPartA, keyPartB);
  
          return map.put(key, value);
      }
docs: Put a value into the map.
  
  @param keyPartA for the key
  @param keyPartB for the key
  @param value    to put into the map
  @return the previous value if found otherwise null