code: public V get(final int keyPartA, final int keyPartB) {
          final long key = compoundKey(keyPartA, keyPartB);
  
          return map.get(key);
      }
docs: Retrieve a value from the map.
  
  @param keyPartA for the key
  @param keyPartB for the key
  @return value matching the key if found or null if not found.