Add the following mutator method to the Point class:

public void flip()

Negates and swaps the x/y coordinates of the Point object. For example, if an object pt initially represents the point (5, -3), after a call of pt.flip(); the object should represent (3,−5). If the same object initially represents the point (4, 17), after a call to pt.flip(); the object should represent (−17,−4).