1. Spring 2010ACS-3913 Ron McFadyen1 Command The complex remote control (many pairs of buttons; null command) Undo … pages 216+ Macro … pages 224+

2. Spring 2010ACS-3913 Ron McFadyen2 Command Undo undo Pressing undo puts the system back to where it was prior to previous command.  Need to “remember” what button was last pressed, and possibly some state information

3. Spring 2010ACS-3913 Ron McFadyen3 Command Undo undo What’s the sequence diagram for : a)turning the fan on and then b)undo-ing that

4. Spring 2010ACS-3913 Ron McFadyen4 Command Undo example from Holub on Patterns (See handout and java programs) Transaction: a unit of work in a database environment – a collection of SQL Select, Update, Insert, Delete commands. A transaction is atomic – executed in its entirety or not at all Last command of a transaction is commit or rollback Commit – effects of transaction made permanent Rollback – effects of transaction are removed so it appears the transaction never even started.

5. Spring 2010ACS-3913 Ron McFadyen5 Command Macro commands undo Suppose we want some commands to comprise a sequence of other commands. Macro A: 1.Turn light on 2.Turn stereo on 3.Turn ceiling fan on low