设计模式之命令模式

(命令模式)

命令模式

将方法调用封装起来，通过封装方法调用，将运算块包装成型。调用次运算的对象不需要关心事情是如何进行的，只要知道如何使用包装成型的方法来完成它就可以。应用于记录日志，或者重复使用这些封装来实现撤销。

命令模式可将“动作的请求者”从“动作的执行者”对象中解耦。

定义

==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。

• receiver 接受者角色
• command 命令角色
• invoker 调用者角色

代码实现

1. Receiver

   public class Light {
       String roomName;
       public Light(String room) {
           this.roomName = room;
       }
       public void on() {
           System.out.println(roomName + " light on...");
       }
   
       public void off() {
           System.out.println(roomName + " light off...");
       }
   
       public void noCommand() {
           System.out.println("no Command...");
       }
   }
   

2. Command

   public interface Command {
       public void execute();
       public void undo();
   }
   
   /**
    *开灯
    */
   public class LightOnCommond implements Command {
       Light light;
       public LightOnCommond(Light light) {
           this.light = light;
       }
       @Override
       public void execute() {
           light.on();
       }
   
       @Override
       public void undo() {
           light.off();
       }
   }
   
   /**
    *关灯
    */
   public class LightOffCommond implements Command {
       Light light;
       public LightOffCommond(Light light) {
           this.light = light;
       }
       @Override
       public void execute() {
           light.off();
       }
   
       @Override
       public void undo() {
           light.on();
       }
   }
   

3. Invoker

   public class RemoteController {
       Command[] onCommands;
       Command[] offCommands;
       Command undoCommand;
   
       public RemoteController() {
           onCommands = new Command[7];
           offCommands = new Command[7];
   
           Command noCommand = new NoCommand();
   
           for (int i = 0; i < 7; i++) {
               onCommands[i] = noCommand;
               offCommands[i] = noCommand;
           }
           undoCommand = noCommand;
       }
   
       public void setCommand(int slot, Command onCommand, Command offCommand) {
           onCommands[slot] = onCommand;
           offCommands[slot] = offCommand;
       }
   
       public void onButtonWasPushed(int slot) {
           onCommands[slot].execute();
           undoCommand = onCommands[slot];
       }
   
       public void offButtonWasPushed(int slot) {
           offCommands[slot].execute();
           undoCommand = offCommands[slot];
       }
   
       public void undoButtonWasPushed() {
           undoCommand.undo();
       }
   
       public String toString() {
           StringBuffer stringBuff = new StringBuffer();
           stringBuff.append("\n------ Remote Controller ------\n");
           for (int i = 0; i < onCommands.length; i++) {
               stringBuff.append("[slot " + i + "] " + onCommands[i].getClass().getName()
                       + "    " + offCommands[i].getClass().getName() + "\n");
           }
           return stringBuff.toString();
       }
   }
   

4. 测试代码

   public class RemoteLoader {
       public static void main(String[] args) {
           RemoteController remoteController = new RemoteController();
           Light livingRoomLight =  new Light("Living Room");
           Light kitchenLight =  new Light("Kitchen");
   
           LightOnCommond livingRoomLightOn = new LightOnCommond(livingRoomLight);
           LightOffCommond livingRoomLightOff = new LightOffCommond(livingRoomLight);
           LightOnCommond kitchenLightOn = new LightOnCommond(kitchenLight);
           LightOffCommond kitchenLightOff = new LightOffCommond(kitchenLight);
   
           remoteController.setCommand(0, livingRoomLightOn, livingRoomLightOff);
           remoteController.setCommand(1, kitchenLightOn, kitchenLightOff);
   
           System.out.println(remoteController);
   
           remoteController.onButtonWasPushed(0);
           remoteController.offButtonWasPushed(0);
           remoteController.onButtonWasPushed(1);
           remoteController.offButtonWasPushed(1);
       }
   }
   

5. 输出结果

   ------ Remote Controller ------
   [slot 0] com.cjn.LightOnCommond    com.cjn.LightOffCommond
   [slot 1] com.cjn.LightOnCommond    com.cjn.LightOffCommond
   [slot 2] com.cjn.NoCommand    com.cjn.NoCommand
   [slot 3] com.cjn.NoCommand    com.cjn.NoCommand
   [slot 4] com.cjn.NoCommand    com.cjn.NoCommand
   [slot 5] com.cjn.NoCommand    com.cjn.NoCommand
   [slot 6] com.cjn.NoCommand    com.cjn.NoCommand
   
   Living Room light on...
   Living Room light off...
   Kitchen light on...
   Kitchen light off...