一、命令模式将请求、命令、动作等封装成对象，这样可以让项目使用这些对象来 参数化其他对象。使得命令的请求者和执行者解耦
二、示例家电自动化遥控器API项目：智能遥控器上有多个开关按钮，可是实现不同家电的控制，也可对新家电进行接入拓展 如果用传统面向对象的模式，则是定义一个遥控的对象，在对象内进行每个按钮的监听，分别判断进行相应的处理 1.电灯对象，控制开关 /** * 电灯对象 */ public class Light { String loc = ""; public Light(String loc) { this.loc = loc; } public void On() { System.out.println(loc + " On"); } public void Off() { System.out.println(loc + " Off"); } } 2.收音机对象，控制开关和音量
/** * 收音机对象 */ public class Stereo { static int volume = 0; public void On() { System.out.println("Stereo On"); } public void Off() { System.out.println("Stereo Off"); } public void SetCd() { System.out.println("Stereo SetCd"); } public void SetVol(int vol) { volume = vol; System.out.println("Stereo volume=" + volume); } public int GetVol() { return volume; } public void Start() { System.out.println("Stereo Start"); } } 3.遥控器对象，进行判断处理
/** * 面向对象模式，遥控对象根据按钮的序号进行相应的处理 */ public class TraditionControl implements Control { Light light; Stereo stereo; public TraditionControl(Light light, Stereo stereo) { this.light = light; this.stereo = stereo; } @Override public void onButton(int slot) { // TODO Auto-generated method stub switch (slot) { case 0: light.On(); break; case 1: stereo.On(); break; case 2: int vol = stereo.GetVol(); if (vol < 11) { stereo.SetVol(++vol); } break; } } @Override public void offButton(int slot) { // TODO Auto-generated method stub switch (slot) { case 0: light.Off(); break; case 1: stereo.Off(); break; case 2: int vol = stereo.GetVol(); if (vol > 0) { stereo.SetVol(--vol); } break; } } @Override public void undoButton() { // TODO Auto-generated method stub } } 缺点：所有操作均在遥控对象内控制，耦合度太高，且如果新增或删减电器则会对整个控制对象进行改动，不利于维护
三、命令模式的实现
1.定义统一的命令方法接口
/** * 命令模式，命令方法接口 */ public interface Command { public void execute(); public void undo(); } 2.创建各自不同的命令对象
/** * 命令模式，电灯打开的命令操作 */ public class LightOnCommand implements Command { private Light light; public LightOnCommand(Light light) { this.light = light; } @Override public void execute() { light.On(); } @Override public void undo() { light.Off(); } } /** * 命令模式，电灯关闭的命令操作 */ public class LightOffCommand implements Command { private Light light; public LightOffCommand(Light light) { this.light=light; } @Override public void execute() { light.Off(); } @Override public void undo() { light.On(); } } 3.遥控器对象对各命令进行抽象处理
/** * 命令模式，所有响应均可抽象成命令，调用时直接调用命令执行方法即可 */ public class CommandModeControl implements Control { private Command[] onCommands; private Command[] offCommands; public CommandModeControl() { onCommands = new Command[5]; offCommands = new Command[5]; Command noCommand = new NoCommand(); for (int i = 0, len = onCommands.length; i < len; i++) { onCommands = noCommand; offCommands = noCommand; } } public void setCommand(int slot, Command onCommand, Command offCommand) { onCommands[slot] = onCommand; offCommands[slot] = offCommand; } // 开 @Override public void onButton(int slot) { onCommands[slot].execute(); } // 关 @Override public void offButton(int slot) { offCommands[slot].execute(); } // 返回 @Override public void undoButton() { } } 4.新增和删减电器时传入相应的实体类进行命令的初始化
/** * 命令模式，便于拓展 */ public class ControlTest { public static void main(String[] args) { CommandModeControl control = new CommandModeControl(); Light bedroomlight = new Light("BedRoom"); Light kitchlight = new Light("Kitch"); Stereo stereo = new Stereo(); LightOnCommand bedroomlighton = new LightOnCommand(bedroomlight); LightOffCommand bedroomlightoff = new LightOffCommand(bedroomlight); LightOnCommand kitchlighton = new LightOnCommand(kitchlight); LightOffCommand kitchlightoff = new LightOffCommand(kitchlight); StereoOnCommand stereoOn = new StereoOnCommand(stereo); StereoOffCommand stereoOff = new StereoOffCommand(stereo); StereoAddVolCommand stereoaddvol = new StereoAddVolCommand(stereo); StereoSubVolCommand stereosubvol = new StereoSubVolCommand(stereo); control.setCommand(0, bedroomlighton, bedroomlightoff); control.setCommand(1, kitchlighton, kitchlightoff); control.setCommand(2, stereoOn, stereoOff); control.setCommand(3, stereoaddvol, stereosubvol); control.onButton(0); control.offButton(0); control.onButton(1); control.offButton(1); control.onButton(2); control.onButton(3); control.offButton(3); control.offButton(2); } }优点： - 命令之间相互分离，互不影响，也便于新命令的接入和删除。
- 即使新增返回按钮，和组合按钮等功能，也易于拓展且不影响其它命令。
| 
收藏
淘帖
踩
奈斯
