public boolean contains(Object o){
  if (!(o instanceof Map.Entry))   return false;
  return c.contains(new UnmodifiableEntry((Map.Entry)o));
}

public boolean contains ( Object o ) { if ( ! ( o instanceof Map . Entry ) ) return false ; return c . contains ( new UnmodifiableEntry ( ( Map . Entry ) o ) ) ; }
this method is overridden to protect the backing set against an object with a nefarious equals function that senses that the equality - candidate is map . entry and calls its setvalue method .
