Command Pattern Chihung Liao Cynthia Jiang

Waiter Order Execute() Hamburger Execute() Hot Dogs Execute() Fries Execute() Cook Make Food()

Hamburger Execute() Hot Dog Execute() Fries Execute() Abstract command (superclass) Concrete command (subclass) Order Execute()

Client Invoker Command Execute() Receiver Action() ConcreteCommand Execute() State

Flexibility and Extensibility Encapsulate a request as an object Compare to C function pointer Decouple the client and receiver by the invoker who ONLY invoke an operation Any request can be cancelled or added in form of stack Request to be executed can be stored as a queue

Translate into JAVA 1 Interface Command: an interface for executing an operation (it could also be an abstract class, refer to the sample code’s comment) Class Client: creates a ConcreteCommand object and set its receiver Class Receiver: who actually DOES things

Translate into JAVA 2 Class Invoker: ask Command to carry out an execution, an agent between ConcreteCommand and Client Class ConcreteCommand implements Command: MUST have the method in Interface Command

QUESTIONS