Java implementation of a combination lock

Please see the attached file.

Objectives
? Group statements into blocks
? Compare integers, doubles, strings, and objects
? Program conditions using Boolean operators and variables
The work should include the following:
? CombinationLock.java
? CombinationLockTest.java
Details
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.
myPositions myPositions after the call setPosition("A") myPositions after the call setPosition("B") myPositions after the call setPosition("D")
"" "A" "AB" "ABD"
Support the following interfacea
/*
Constructs a lock with a given combination. The state is initially
closed (false) and the positions is (are?) an empty string ("").
@param combination is a string with three uppercase letters A..Z
*/
public CombinationLock( String combination )

/*
Set the dial to a position. See chart above for an example.
@param position is a string consisting of a single uppercase letter A..Z
*/
public void setPosition(String aPosition)

/*
Try unlocking the lock. If the lock is closed and the length of the
positions is >= 3, test to see if the combination is equal to the
last three positions. If they are equal, open the lock otherwise
leave it unchanged.
*/
public void unlock()

/*
Check whether the lock is unlocked.
@return true if the lock is currently open.
*/
public boolean isOpen()

/*
Close the lock and start over by setting the state and the
positions to the empty string ""
*/
public void startOver()
You will need the following instance fields.
private boolean myState; // myState is true if the lock is open and
// false otherwise
private String myCombination; // A three character string
// representing the combination
private String myPositions; // A string that represents the positions
// set on the dial. This string can
// be any length.
The CombinationLockTest Class
? Instantiate a lock with the combination "ABC".
? Try opening the lock by using the setPosition() method 3 times with the following sequence "A","B", "D".
? Try to unlock the lock using the unlock() method.
? Make sure the lock did not open by printing the result of the isOpen() method.
? If the lock is open starOver() (Conditional statement)
? Try opening the lock by using the setPosition() method 2 times with "A", "B".
? Try to unlock the lock using the unlock() method.
? Make sure the lock did not open by printing the result of the isOpen() method.
? If the lock is open startOver() (Conditional statement)
? Try opening the lock by using the setPosition() method 1 time with "C".
? Use unlock().
? Make sure the lock is open by printing the result of the isOpen() method.
? If the lock is open startOver() (Conditional statement).
? Make sure the lock did not open by printing the result of the isOpen() method.
? Try opening the lock by using the setPosition() method 4 times with the following "A", "A", "B", "C".
? Try to unlock the lock using the unlock() method.
? Make sure the lock is open by printing the result of the isOpen() method.