设计模式学习笔记——命令模式

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。命令模式也支持可撤销的操作。

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实现命令接口

public interface Command {    public void execute();    public void undo();}

目标类以及命令封装

public class Light {    private String name;    public Light(String name) {        this.name = name;    }      public void on(){        System.out.println(name+" Light is on!");    }    public void off(){        System.out.println(name+" Light is off!");    }}

public class LightOnCommand implements Command {    Light light;    public LightOnCommand(Light light) {        this.light = light;    }    public void execute() {        light.on();    }    public void undo() {        light.off();    }}

public class LightOffCommand implements Command {    Light light;    public LightOffCommand(Light light) {        this.light = light;    }    public void execute() {        light.off();    }    public void undo() {        light.on();    }}

实现一个空命令

public class NoCommand implements Command {    public void execute() {}}

遥控器类

public class RemoteControl {    Command[] onCommands;    Command[] offCommands;    Command undoCommand; // 前一个命令    public RemoteControl() {        onCommands = new Command[6];        offCommands = new Command[6];        Command noCommand = new NoCommand();        for(int i = 0; i < 6; i++) {            onCommands[i] = noCommand;            offCommands[i] = noCommand;        }        undoCommand = noCommand;    }    public void setCommand(int pos, Command onCommand, Command offCommand) {        onCommands[pos] = onCommand;        offCommands[pos] = offCommand;    }    public void onButtonWasPushed(int pos) {        onCommands[pos].execute();        undoCommand = onCommands[pos];    }    public void offButtonWasPushed(int pos) {        offCommands[pos].execute();        undoCommand = offCommands[pos];    }    public void undoButtonWasPushed() {        undoCommand.undo();    }}

Client

public class Client {    public static void main(String[] args) {        RemoteControl remoteControl = new RemoteControl();        Light livingRoomLight = new Light("Living Room");        LightOnCommand livingRoomLightOn =                    new LightOnCommand(livingRoomLight);        LightOffCommand livingRoomLightOff =                    new LightOffCommand(livingRoomLight);        remoteControl.setCommand(0, livingRoomLightOn, livingRoomLightOff);        remoteControl.onButtonWasPushed(0);        remoteControl.offButtonWasPushed(0);        remoteControl.undoButtonWasPushed();            }}

输出结果如下：

Living Room Light is on!
Living Room Light is off!
Living Room Light is on!