CSC/ECE 517 Fall 2010/ch4 4f sv

What is Command Pattern ?

The command pattern is a design pattern in which an object is used to represent and encapsulate all the information needed to call a method at a later time. This information includes the method name, the object that owns the method and values for the method parameters. It encapsulates a request as an object and gives it a known public interface. It ensures that every object receives its own commands and provides a decoupling between sender and receiver. In this case a sender is an object that invokes an operation, and a receiver is an object that receives the request and acts on it.

Why and When do we use a Command Pattern?

Command Pattern comes into picture when there is a need to store objects behaviour as a command and its state. The Command design pattern encapsulates commands (method calls) in objects allowing us to issue requests without knowing the requested operation or the requesting object. Command design pattern provides the options to queue commands, undo/redo actions and other manipulations.

There are several benefits of using the Command pattern:

> It provides encapsulation of application logic so that it can be executed at a different point of time. > It allows to execute the application in separate contexts, such as in a different thread or using a different state by separating the application logic and context. > The separation between application logic and context allows to easier exchange the application logic.