code: public boolean containsKey(Object key) {
          return isValidKey(key) && vals[((Enum<?>)key).ordinal()] != null;
      }
docs: Returns <tt>true</tt> if this map contains a mapping for the specified
  key.
  
  @param key the key whose presence in this map is to be tested
  @return <tt>true</tt> if this map contains a mapping for the specified
  key