Command Pattern 命令模式

Definition

Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
命令模式将“请求”封装成对象，以便使用不同的请求、队列或者日志来参数化其他对象，同时支持可撤消的操作。

Participants

The classes and objects participating in this pattern are:

Command

• declares an interface for executing an operation

ConcreteCommand

• defines a binding between a Receiver object and an action
• implements Execute by invoking the corresponding operation(s) on Receiver

Client

• creates a ConcreteCommand object and sets its receiver

Invoker

• asks the command to carry out the request

Receiver

• knows how to perform the operations associated with carrying out the request.