Java设计模式之命令模式

文章目录 Java 设计模式之命令模式概述UML代码实现简单实现复杂实现

Java 设计模式之命令模式 概述 命令模式(Command)：将一个请求封装为一个对象，从而使你可用不同的请求对客户进行参数化；对请求排队或记录请求日志，以及支持可撤销的操作。敏捷开发原则告诉我们，不要为代码添加基于猜测的、实际不需要的功能。如果不清楚一个系统是否需要命令模式，一般就不要着急去实现它，事实上，在需要的时候通过重构实现这个模式并不困难，只有在真正需要如撤销／恢复操作等功能时，把原来的代码重构为命令模式才有意义。 UML

Command：命令接口，定义执行操作的通用接口。ConcreteCommand：具体命令类，实现具体的命令操作，持有接受者对象。Receiver：接收者累，实际执行操作的对象。Invoker：调用者，触发命令的对象。 代码实现 简单实现

定义命令接口：

public interface Command { void execute(); }

定义具体命令类：

public class LightOffCommand implements Command { private Light light; public LightOffCommand(Light light) { this.light = light; } @Override public void execute() { light.turnOff(); } } public class LightOnCommand implements Command { private Light light; public LightOnCommand(Light light) { this.light = light; } @Override public void execute() { light.turnOn(); } }

定义接收者类：

public class Light { public void turnOn() { System.out.println("开灯"); } public void turnOff() { System.out.println("关灯"); } }

定义调用者类：

public class RemoteControl { private Command command; public void setCommand(Command command) { this mand = command; } public void pressButton() { command.execute(); } }

使用：

public class Client { public static void main(String[] args) { Light light = new Light(); Command lightOn = new LightOnCommand(light); Command lightOff = new LightOffCommand(light); RemoteControl control = new RemoteControl(); control.setCommand(lightOn); control.pressButton(); control.setCommand(lightOff); control.pressButton(); } }

输出：

开灯 关灯 复杂实现

定义抽象命令类：

abstract class Command { protected RoastCook receiver; public Command(RoastCook receiver) { this.receiver = receiver; } abstract void execute(); }

定义接收者类：

public class RoastCook { public void bakeMeet() { System.out.println("烤肉"); } public void bakeFish() { System.out.println("烤鱼"); } }

定义具体命令类：

public class RoastFishCommand extends Command { public RoastFishCommand(RoastCook receiver) { super(receiver); } @Override void execute() { receiver.bakeFish(); } } public class RoastMeatCommand extends Command { public RoastMeatCommand(RoastCook receiver) { super(receiver); } @Override void execute() { receiver.bakeMeet(); } }

定义调用者类：

public class Waiter { private ArrayList<Command> orders = new ArrayList<>(); private Command command; // 下单 public void setOrder(Command command) { String className = command.getClass().getSimpleName(); if (className.equals("RoastFishCommand")) { System.out.println("下单：" + "烤鱼"); } else { System.out.println("下单：" + "烤肉"); } orders.add(command); } // 取消订单 public void cancelOrder(Command command) { String className = command.getClass().getSimpleName(); if (className.equals("RoastFishCommand")) { System.out.println("取消：" + "烤鱼"); } else { System.out.println("取消：" + "烤肉"); } orders.remove(command); } // 通知 public void notifyCommand() { for (Command command : orders) { command.execute(); } } }

使用：

public class Client { public static void main(String[] args) { RoastCook receiver = new RoastCook(); Command roastMeatCommand = new RoastMeatCommand(receiver); Command roastFishCommand1 = new RoastFishCommand(receiver); Command roastFishCommand2 = new RoastFishCommand(receiver); Command roastFishCommand3 = new RoastFishCommand(receiver); Waiter waiter = new Waiter(); waiter.setOrder(roastFishCommand1); waiter.setOrder(roastFishCommand2); waiter.setOrder(roastMeatCommand); waiter.setOrder(roastFishCommand3); waiter.cancelOrder(roastFishCommand2); waiter.notifyCommand(); } }

输出：

下单：烤鱼 下单：烤鱼 下单：烤肉 下单：烤鱼 取消：烤鱼 烤鱼 烤肉 烤鱼