Implement a combination lock class. A combination lock has a dial with 26 positions labeled A . . . Z. The dial needs to be set three times. If it is set to the correct combination, the lock can be opened. When the lock is closed again, the combination can be entered again. If a user sets the dial more than three times, the last three settings determine whether the lock can be opened. An important part of this exercise is to implement a suitable interface for the CombinationLock class.