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。



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!