In software systems, "Behavior requester" and "Behavior implementer" usually present a kind of "Tight coupling". But in some situations, such as "recording, undo/redo, transaction" and other processing of behaviors, this kind of tight coupling that cannot resist changes is inappropriate. In this case, how to decouple the "behavior requester" from the "behavior implementer"? Abstract a set of behaviors into objects , achieve loose coupling between the two . This isCommand Pattern
Class Diagram
#
public interface ICommand { void execute(); }
public class ConcreteCommand implements ICommand { private Receiver receiver; public ConcreteCommand(Receiver receiver) { this.receiver = receiver; } @Override public void execute() { this.receiver.action(); } }
public class Receiver { public void action() { System.out.println("receiver do something"); } }
public class Invoker { private ICommand command; public Invoker(ICommand command) { this.command = command; } public void invoke() { this.command.execute(); } }
/* * 命令(Command)模式 * 请求与执行 分离 * 可以多个命令接口的实现类,隐藏真实的被调用方 */ public class Test { public static void main(String[] args) { Receiver receiver = new Receiver();//真正的执行者 ICommand command = new ConcreteCommand(receiver);//具体命令 Invoker invoker = new Invoker(command );//调用者 invoker.invoke(); } }
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