java设计模式(五)—命令模式

1.概念：

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它对象。命令模式也支持可撤销操作。

自己理解：在特定接收者上绑定一组动作来封装一个请求（成为对象），并只暴露出一个execute()方法。然后将该对象做为参数传给其它类或对象（调用者），当调用者调用execute()的时候，接收者就会进行相应的动作。

2.作用

一个命令对象通过在特定接收者上绑定一组动作来封装一个请求。要达到这一点，命令对象将动作和接收者包进对象中。这个对象只暴露出一个execute()方法，当此方法被调用的时候，接收者就会进行这些动作。

要点：

(1)命令模式将发出请求的对象和执行请求的对象解耦。

(2)在被解耦的两者之间是通过命令对象进行沟通的。命令对象封装了接收者和一个或一组对作。

(3)调用者通过调用命令对象的exceute()发出请求，这会使得接收者的动作被调用。

(4)调用者会接收命令做为参数，甚至在运行时动态的进行。

3.依赖原则

(1)封装变化

(2)多用组合，少用继承

(3)针对接口编程，而不是具体的实现

(4)为交互对象之间的松耦合设计而努力

(5)类应该对扩展开放，对修改关闭

(6)依赖抽象，不依赖具体类

4.具体实现

4.1 类图



4.2 代码实现

//测试类，代表客户
package test;

import invoke.RemoteControl;
import receiver.GarageDoor;
import receiver.Light;
import command.GarageDoorCloseCommand;
import command.GarageDoorOpenCommand;
import command.LightOffCommand;
import command.LightOnCommand;

public class RemoteLoader {

public static void main(String args[]){
RemoteControl remoteControl = new RemoteControl();
Light light = new Light();
LightOnCommand lightOnCommand = new LightOnCommand(light);
LightOffCommand lightOffCommand = new LightOffCommand(light);
remoteControl.setCommand(0, lightOnCommand, lightOffCommand);
remoteControl.onButtonwasPressed(0);
remoteControl.offButtonwasPressed(0);

GarageDoor garageDoor = new GarageDoor();
GarageDoorOpenCommand garageDoorOpenCommand = new GarageDoorOpenCommand(garageDoor);
GarageDoorCloseCommand garageDoorCloseCommand = new GarageDoorCloseCommand(garageDoor);
remoteControl.setCommand(1, garageDoorOpenCommand, garageDoorCloseCommand);
remoteControl.onButtonwasPressed(1);
remoteControl.offButtonwasPressed(1);
}
}

//接收者
package receiver;

public class GarageDoor {

public GarageDoor() {

}

public void open() {
System.out.println("grageDoor is open");
}

public void close() {
System.out.println("grageDoor is close");

}

}

//接收者
package receiver;

public class Light {

public Light() {

}

public void on() {
System.out.println("light is on");
}

public void off() {
System.out.println("light is off");
}

}

//调用者
package invoke;

import command.Command;
import command.NoCommand;

public class RemoteControl {

Command[] onCommands;
Command[] offCommands;

public RemoteControl(){
onCommands = new Command[7];
offCommands = new Command[7];
for(int i=0;i<7;i++){
onCommands[i] = new NoCommand();
offCommands[i] = new NoCommand();
}

}
public void setCommand(int i ,Command onCommand,Command offCommand) {
onCommands[i] = onCommand;
offCommands[i] = offCommand;
}
public void onButtonwasPressed(int i) {
onCommands[i].execute();
}
public void offButtonwasPressed(int i){
offCommands[i].execute();
}
}

//命令对象：封装接收者和执行动作。
package command;

public interface Command {
public void execute();
}

package command;

import receiver.GarageDoor;

public class GarageDoorCloseCommand implements Command {

GarageDoor garageDoor;

public GarageDoorCloseCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}

@Override
public void execute() {
garageDoor.close();
}

}
package command;

import receiver.GarageDoor;

public class GarageDoorOpenCommand implements Command {

GarageDoor garageDoor;

public GarageDoorOpenCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}

@Override
public void execute() {
garageDoor.open();
}

}
package command;

import receiver.Light;

public class LightOffCommand implements Command {

Light light;

public LightOffCommand(Light light) {
this.light = light;
}

public void execute() {
light.off();
}

}
package command;

import receiver.Light;

public class LightOnCommand implements Command {

Light light;

public LightOnCommand(Light light) {
this.light = light;
}

public void execute() {
light.on();
}

}

package command;

public class NoCommand implements Command {

@Override
public void execute() {
System.out.println("no");
}

}