code: public boolean containsKey(Object key) {
          if (key instanceof Number) {
              return containsKey( ((Number)key).intValue() );
          }
          else {
              return false;
          }
      }
docs: Returns <tt>true</tt> if this map contains a mapping for the specified
  key.
  
  @return <tt>true</tt> if this map contains a mapping for the specified
  key.
  @param key key whose presence in this Map is to be tested.