1. March 200692.3913 Ron McFadyen1 Command The command pattern encapsulates a request or unit of work into an object. An invoker will ask a concrete command to perform its function and the concrete command will in turn ask some receiver to perform a pre-determined action.

2. March 200692.3913 Ron McFadyen2 Command – generic class diagram «Interface» Command Concrete Command Receiver Invoker Command Concrete commandreceiver command action1() action2() execute() setCommand() invoker

3. March 200692.3913 Ron McFadyen3 Command – text example «Interface » Command lightOn Command Light Remote control Command Concrete command receiver command on() off() execute() setCommand() invoker lightOff Command execute() Concrete command null Command execute() Concrete command

4. March 200692.3913 Ron McFadyen4 Command - behaviour :Light:RemoteControl execute() lightOn() execute() lightOff() :LightOn Command :LightOff Command :null Command execute()

5. March 200692.3913 Ron McFadyen5 Command Example: User interfaces typically give you ways to issue a particular command Java Swing classes use the command pattern to perform application-specific functionality. Action objects are used. Button classes, menu items, etc. maintain a reference to an action defined by the Action interface. Whenever a Swing component activates, it calls its action’s (command’s) actionPerformed() method (execute() method).

6. March 200692.3913 Ron McFadyen6 Command Example: Consider the handout having to do with executing transactions in an SQL environment