Command Pattern的目的在于分離命令的發(fā)出者和命令的執(zhí)行者。就好比在飯店吃飯，作為客戶（命令的發(fā)出者），你無(wú)需直接跟廚師說明要點(diǎn)什么菜，只要把菜單給服務(wù)員就行了，而服務(wù)員并不負(fù)責(zé)燒菜，只要把菜單交給廚師（執(zhí)行者）即可，廚師會(huì)根據(jù)菜單做菜了。這兩者被分離了。
下面來實(shí)現(xiàn)這個(gè)點(diǎn)菜的過程：我們要點(diǎn)兩個(gè)菜，burger和malt。最簡(jiǎn)單的實(shí)現(xiàn)如下：
package javaapplication29;
public class Main {
public static void main(String[] args) {
Cook cook = new Cook();
cook.burger();
cook.malt();
}
}
class Cook {
void burger() {
System.out.println("burger maked");
}
void malt() {
System.out.println("malt maked");
}
}
這里有個(gè)問題：我們要點(diǎn)什么菜，是寫在主函數(shù)里的。如果要點(diǎn)的菜有所改變，比如第二個(gè)人要點(diǎn)菜，點(diǎn)其他菜，那么主函數(shù)里的代碼就要重寫。這里就出現(xiàn)了所謂的“變化沒有被封裝”的問題。這里的代碼實(shí)現(xiàn)過程就好比顧客直接跟廚師說要吃什么菜一樣。
這里我們引入“菜單”，所謂菜單的作用在于：把變化的“點(diǎn)什么菜”封裝到菜單這個(gè)對(duì)象里面去。實(shí)際上就是把主函數(shù)中變化的部分封裝到一個(gè)類中去了。
package javaapplication29;
public class Main {
public static void main(String[] args) {
Cook cook = new Cook();
Manu1 manu1 = new Manu1(cook);
manu1.orderup();
}
}
class Cook {
void burger() {
System.out.println("burger maked");
}
void malt() {
System.out.println("malt maked");
}
}
class Manu1 {
Cook cook;
public Manu1(Cook cook) {
this.cook = cook;
}
public void orderup() {
cook.burger();
cook.malt();
}
}
如果有第二個(gè)菜單，我們就再寫第二個(gè)類Manu2出來：
package javaapplication29;
public class Main {
public static void main(String[] args) {
Cook cook = new Cook();
Manu1 manu1 = new Manu1(cook);
manu1.orderup();
Manu2 manu2=new Manu2(cook);
manu2.orderup();
}
}
class Cook {
void burger() {
System.out.println("burger maked");
}
void malt() {
System.out.println("malt maked");
}
}
class Manu1 {
Cook cook;
public Manu1(Cook cook) {
this.cook = cook;
}
public void orderup() {
cook.burger();
cook.malt();
}
}
class Manu2 {
Cook cook;
public Manu2(Cook cook) {
this.cook = cook;
}
public void orderup() {
cook.burger();
}
}
這里我們發(fā)現(xiàn)Manu1和Manu2兩個(gè)類形式幾乎相通，只是orderup（）函數(shù)內(nèi)執(zhí)行的東西不一樣。在主函數(shù)中，要執(zhí)行第二個(gè)菜單還得重新生成一個(gè)對(duì)象，Manu2 manu2=new Manu2(cook); 而不能直接切換，manu1=new Manu2(cook); 這很不爽，由此很容易想到用一個(gè)父類，讓Manu1，Manu2繼承之，如下：
package javaapplication29;
public class Main {
public static void main(String[] args) {
Cook cook = new Cook();
Manu manu = new Manu1(cook);
manu.orderup();
manu = new Manu2(cook);
manu.orderup();
}
}
class Cook {
void burger() {
System.out.println("burger maked");
}
void malt() {
System.out.println("malt maked");
}
}
abstract class Manu {
abstract public void orderup();
}
class Manu1 extends Manu {
Cook cook;
public Manu1(Cook cook) {
this.cook = cook;
}
public void orderup() {
cook.burger();
cook.malt();
}
}
class Manu2 extends Manu {
Cook cook;
public Manu2(Cook cook) {
this.cook = cook;
}
public void orderup() {
cook.burger();
}
}
這個(gè)實(shí)際上變成工廠模式了。我們看到主函數(shù)中：
Manu manu = new Manu1(cook);
manu.orderup();
這里，命令的發(fā)出是通過菜單的orderup方法發(fā)出的。可實(shí)際中，菜單是不能發(fā)命令的，而是客戶通過服務(wù)員發(fā)命令的。我們需要一個(gè)Waitress這個(gè)對(duì)象來裝載各種菜單，并對(duì)廚師發(fā)出點(diǎn)菜的命令（通過調(diào)用Manu的orderup方法）。如下：
package javaapplication29;
public class Main {
public static void main(String[] args) {
Cook cook = new Cook();
Waitress waitress = new Waitress();
Manu manu = new Manu1(cook);
waitress.setManu(manu);
waitress.callCook();
manu = new Manu2(cook);
waitress.setManu(manu);
waitress.callCook();
}
}
class Cook {
void burger() {
System.out.println("burger maked");
}
void malt() {
System.out.println("malt maked");
}
}
abstract class Manu {
abstract public void orderup();
}
class Manu1 extends Manu {
Cook cook;
public Manu1(Cook cook) {
this.cook = cook;
}
public void orderup() {
cook.burger();
cook.malt();
}
}
class Manu2 extends Manu {
Cook cook;
public Manu2(Cook cook) {
this.cook = cook;
}
public void orderup() {
cook.burger();
}
}
class Waitress {
Manu manu;
public void setManu(Manu manu) {
this.manu = manu;
}
public void callCook() {
manu.orderup();
}
}
在這個(gè)程序里，我們發(fā)現(xiàn)其實(shí)Waitress在主程序中只知道要callCook（）
waitress.callCook();
而她并不知道callCook（）在具體執(zhí)行什么，因?yàn)?/span>Waitress類中的manu是一個(gè)抽象類的對(duì)象，而callCook（）方法中的manu.orderup() 是抽象方法，鬼知道它的具體實(shí)現(xiàn)是什么。
這就是Command Pattern的目的：把命令封裝成對(duì)象（Manu1，Manu2），讓調(diào)用命令的人（Waitress）裝載該對(duì)象（setManu），隨時(shí)可以發(fā)出該命令（callCook）。而調(diào)用命令的人，并不知道該命令的具體執(zhí)行過程。
這有點(diǎn)類似于給工廠模式中的抽象工廠添加了一個(gè)裝載器。值得注意的是，在工廠模式中，頂層的抽象工廠一般是抽象類，而在命令模式中，頂層的一般都是接口。其實(shí)到底用抽象類還是接口并不重要！因?yàn)樵谀撤N程度上，他們都是Interface。到底用哪個(gè)，根據(jù)需要使用，畢竟可以實(shí)現(xiàn)多接口而不能繼承多個(gè)抽象類。Command Pattern的關(guān)鍵不在于這里，而在于裝載器和工廠模式的結(jié)合。
《head first design pattern》上要實(shí)現(xiàn)一個(gè)遠(yuǎn)程控制器，思路跟上面一樣。代碼如下所示：
package javaapplication30;
public class Main {
public static void main(String[] args) {
Light light = new Light();
Command command = new LightOnCommand(light);
RemoteControl rc = new RemoteControl();
rc.setControl(command);
rc.ButtonDown();
GarageDoor garageDoor = new GarageDoor();
command = new GarageDoorOpenCommand(garageDoor);
rc.setControl(command);
rc.ButtonDown();
}
}
class Light {
public void on() {
System.out.println("turn Light on.");
}
}
class GarageDoor {
public void open() {
System.out.println("open GarageDoor");
}
}
interface Command {
public void execute();
}
class LightOnCommand implements Command {
Light light;
LightOnCommand(Light light) {
this.light = light;
}
public void execute() {
light.on();
}
}
class GarageDoorOpenCommand implements Command {
GarageDoor garageDoor;
GarageDoorOpenCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.open();
}
}
class RemoteControl {
Command command;
public void setControl(Command command) {
this.command = command;
}
public void ButtonDown() {
command.execute();
}
}
以上設(shè)計(jì)出的遠(yuǎn)程控制器只有一個(gè)slot，對(duì)應(yīng)一個(gè)按鈕。現(xiàn)在如果要實(shí)現(xiàn)7個(gè)slot，每個(gè)slot對(duì)應(yīng)一個(gè)“打開”按鈕，則需要把RemoteControl這個(gè)類改動(dòng)一下：
package javaapplication30;
public class Main {
public static void main(String[] args) {
Light light = new Light();
GarageDoor garageDoor = new GarageDoor();
RemoteControl rc = new RemoteControl();
Command command = new LightOnCommand(light);
rc.setControl(0, command);
command = new GarageDoorOpenCommand(garageDoor);
rc.setControl(1, command);
rc.buttonDown(0);
rc.buttonDown(1);
}
}
class Light {
public void on() {
System.out.println("turn Light on.");
}
}
class GarageDoor {
public void open() {
System.out.println("open GarageDoor");
}
}
interface Command {
public void execute();
}
class noCommand implements Command {
public void execute() {
System.out.println("no command here.");
}
}
class LightOnCommand implements Command {
Light light;
LightOnCommand(Light light) {
this.light = light;
}
public void execute() {
light.on();
}
}
class GarageDoorOpenCommand implements Command {
GarageDoor garageDoor;
GarageDoorOpenCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.open();
}
}
class RemoteControl {
Command[] onCommands;
Command noCommand = new noCommand();
public RemoteControl() {
onCommands = new Command[7];
for (int i = 0; i < 7; i++) {
onCommands[i] = noCommand; //初始化7個(gè)槽對(duì)應(yīng)的按鈕指令為空
}
}
public void setControl(int slot, Command command) {
onCommands[slot] = command;
}
public void buttonDown(int slot) {
onCommands[slot].execute();
}
}
對(duì)比之前的只有一個(gè)slot的程序，RemoteControl類添加了一個(gè)初始化作用的構(gòu)造函數(shù)，并在每個(gè)方法的參數(shù)表里添加了slot參數(shù)。
如果想要有7個(gè)slot，每個(gè)slot都對(duì)應(yīng)“開”、“關(guān)”兩個(gè)按鈕，則同理，講RemoteControl中的參數(shù)再各增加一個(gè)即可，如下：
package javaapplication30;
public class Main {
public static void main(String[] args) {
Light light = new Light();
GarageDoor garageDoor = new GarageDoor();
RemoteControl rc = new RemoteControl();
Command onCommand = new LightOnCommand(light);
Command offCommand = new LightOffCommand(light);
rc.setControl(0, onCommand, offCommand);
onCommand = new GarageDoorOpenCommand(garageDoor);
offCommand = new GarageDoorCloseCommand(garageDoor);
rc.setControl(1, onCommand, offCommand);
rc.onButtonDown(0);
rc.offButtonDown(1);
rc.offButtonDown(0);
rc.onButtonDown(1);
}
}
class Light {
public void on() {
System.out.println("turn Light on.");
}
void off() {
System.out.println("turn light off");
}
}
class GarageDoor {
public void open() {
System.out.println("open GarageDoor");
}
public void close() {
System.out.println("close GarageDoor");
}
}
interface Command {
public void execute();
}
class noCommand implements Command {
public void execute() {
System.out.println("no command here.");
}
}
class LightOnCommand implements Command {
Light light;
LightOnCommand(Light light) {
this.light = light;
}
public void execute() {
light.on();
}
}
class LightOffCommand implements Command {
Light light;
LightOffCommand(Light light) {
this.light = light;
}
public void execute() {
light.off();
}
}
class GarageDoorOpenCommand implements Command {
GarageDoor garageDoor;
GarageDoorOpenCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.open();
}
}
class GarageDoorCloseCommand implements Command {
GarageDoor garageDoor;
GarageDoorCloseCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.close();
}
}
class RemoteControl {
Command[] onCommands;
Command[] offCommands;
Command noCommand = new noCommand();
public RemoteControl() {
onCommands = new Command[7];
offCommands = new Command[7];
for (int i = 0; i < 7; i++) {
onCommands[i] = noCommand;
offCommands[i] = noCommand;
}
}
public void setControl(int slot, Command onCommand, Command offCommand) {
onCommands[slot] = onCommand;
offCommands[slot] = offCommand;
}
public void onButtonDown(int slot) {
onCommands[slot].execute();
}
public void offButtonDown(int slot) {
offCommands[slot].execute();
}
}
如何給上面的程序添加一個(gè)undo按鈕呢，就是撤銷上一次的操作。
（1） 我們要給Command接口以及它的所有實(shí)現(xiàn)體（LightOnCommand, GarageCloseCommand等）添加undo（）方法，undo執(zhí)行的內(nèi)容就是和execute（）執(zhí)行相反的即可。
（2） 我們還在RemoteControl類中，想辦法記錄最后一次執(zhí)行的是哪個(gè)XXXCommand
實(shí)現(xiàn)如下：
package javaapplication30;
public class Main {
public static void main(String[] args) {
Light light = new Light();
GarageDoor garageDoor = new GarageDoor();
RemoteControl rc = new RemoteControl();
Command onCommand = new LightOnCommand(light);
Command offCommand = new LightOffCommand(light);
rc.setControl(0, onCommand, offCommand);
onCommand = new GarageDoorOpenCommand(garageDoor);
offCommand = new GarageDoorCloseCommand(garageDoor);
rc.setControl(1, onCommand, offCommand);
rc.onButtonDown(0);
rc.undoButtonDown();
rc.offButtonDown(1);
rc.offButtonDown(0);
rc.onButtonDown(1);
rc.undoButtonDown();
}
}
class Light {
public void on() {
System.out.println("turn Light on.");
}
void off() {
System.out.println("turn light off");
}
}
class GarageDoor {
public void open() {
System.out.println("open GarageDoor");
}
public void close() {
System.out.println("close GarageDoor");
}
}
interface Command {
public void execute();
public void undo();
}
class noCommand implements Command {
public void execute() {
System.out.println("no command here.");
}
public void undo() {
System.out.println("no command here.");
}
}
class LightOnCommand implements Command {
Light light;
LightOnCommand(Light light) {
this.light = light;
}
public void execute() {
light.on();
}
public void undo() {
light.off();
}
}
class LightOffCommand implements Command {
Light light;
LightOffCommand(Light light) {
this.light = light;
}
public void execute() {
light.off();
}
public void undo() {
light.on();
}
}
class GarageDoorOpenCommand implements Command {
GarageDoor garageDoor;
GarageDoorOpenCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.open();
}
public void undo() {
garageDoor.close();
}
}
class GarageDoorCloseCommand implements Command {
GarageDoor garageDoor;
GarageDoorCloseCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.close();
}
public void undo() {
garageDoor.open();
}
}
class RemoteControl {
Command[] onCommands;
Command[] offCommands;
Command noCommand = new noCommand();
Command lastCommand;
public RemoteControl() {
onCommands = new Command[7];
offCommands = new Command[7];
for (int i = 0; i < 7; i++) {
onCommands[i] = noCommand;
offCommands[i] = noCommand;
}
}
public void setControl(int slot, Command onCommand, Command offCommand) {
onCommands[slot] = onCommand;
offCommands[slot] = offCommand;
}
public void onButtonDown(int slot) {
onCommands[slot].execute();
lastCommand = onCommands[slot];
}
public void offButtonDown(int slot) {
offCommands[slot].execute();
lastCommand = offCommands[slot];
}
public void undoButtonDown() {
lastCommand.undo();
}
}
電器的功能可能不止“開”和“關(guān)”，比如電風(fēng)扇，有換擋功能。對(duì)于電風(fēng)扇的High，Medium，Low三個(gè)檔位，每個(gè)要寫一個(gè)單獨(dú)的FanXXXCommand類。對(duì)每個(gè)檔位做undo的時(shí)候，不能直接簡(jiǎn)單的取反，要找到上一次的檔位才行。
package javaapplication30;
public class Main {
public static void main(String[] args) {
Light light = new Light();
GarageDoor garageDoor = new GarageDoor();
RemoteControl rc = new RemoteControl();
Command onCommand = new LightOnCommand(light);
Command offCommand = new LightOffCommand(light);
rc.setControl(0, onCommand, offCommand);
onCommand = new GarageDoorOpenCommand(garageDoor);
offCommand = new GarageDoorCloseCommand(garageDoor);
rc.setControl(1, onCommand, offCommand);
rc.onButtonDown(0);
rc.undoButtonDown();
rc.offButtonDown(1);
rc.offButtonDown(0);
rc.onButtonDown(1);
rc.undoButtonDown();
Fan fan = new Fan();
onCommand = new FanHighCommand(fan);
offCommand = new FanOffCommand(fan);
rc.setControl(2, onCommand, offCommand);
rc.onButtonDown(2);
rc.offButtonDown(2);
rc.undoButtonDown();
}
}
class Light {
public void on() {
System.out.println("turn Light on.");
}
void off() {
System.out.println("turn light off");
}
}
class GarageDoor {
public void open() {
System.out.println("open GarageDoor");
}
public void close() {
System.out.println("close GarageDoor");
}
}
class Fan {
public final int HIGH = 3;
public final int MEDIUM = 2;
public final int LOW = 1;
public final int OFF = 0;
public int speed = 0;
public void high() {
speed = HIGH;
System.out.println("Fan's speed is " + speed);
}
public void low() {
speed = LOW;
System.out.println("Fan's speed is " + speed);
}
public void medium() {
speed = MEDIUM;
System.out.println("Fan's speed is " + speed);
}
public void off() {
speed = OFF;
System.out.println("Fan's speed is " + speed);
}
public int getSpeed() {
return speed;
}
}
interface Command {
public void execute();
public void undo();
}
class noCommand implements Command {
public void execute() {
System.out.println("no command here.");
}
public void undo() {
System.out.println("no command here.");
}
}
class FanHighCommand implements Command {
Fan fan;
int preSpeed;
FanHighCommand(Fan fan) {
this.fan = fan;
}
public void execute() {
preSpeed = fan.getSpeed();
fan.high();
}
public void undo() {
if (preSpeed == fan.HIGH) {
fan.high();
}
else if (preSpeed == fan.MEDIUM) {
fan.medium();
}
else if (preSpeed == fan.LOW) {
fan.low();
}
else if (preSpeed == fan.OFF) {
fan.off();
}
}
}
class FanOffCommand implements Command {
Fan fan;
int preSpeed;
FanOffCommand(Fan fan) {
this.fan = fan;
}
public void execute() {
preSpeed = fan.getSpeed();
fan.off();
}
public void undo() {
if (preSpeed == fan.HIGH) {
fan.high();
}
else if (preSpeed == fan.MEDIUM) {
fan.medium();
}
else if (preSpeed == fan.LOW) {
fan.low();
}
else if (preSpeed == fan.OFF) {
fan.off();
}
}
}
class LightOnCommand implements Command {
Light light;
LightOnCommand(Light light) {
this.light = light;
}
public void execute() {
light.on();
}
public void undo() {
light.off();
}
}
class LightOffCommand implements Command {
Light light;
LightOffCommand(Light light) {
this.light = light;
}
public void execute() {
light.off();
}
public void undo() {
light.on();
}
}
class GarageDoorOpenCommand implements Command {
GarageDoor garageDoor;
GarageDoorOpenCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.open();
}
public void undo() {
garageDoor.close();
}
}
class GarageDoorCloseCommand implements Command {
GarageDoor garageDoor;
GarageDoorCloseCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.close();
}
public void undo() {
garageDoor.open();
}
}
class RemoteControl {
Command[] onCommands;
Command[] offCommands;
Command noCommand = new noCommand();
Command lastCommand;
public RemoteControl() {
onCommands = new Command[7];
offCommands = new Command[7];
for (int i = 0; i < 7; i++) {
onCommands[i] = noCommand;
offCommands[i] = noCommand;
}
}
public void setControl(int slot, Command onCommand, Command offCommand) {
onCommands[slot] = onCommand;
offCommands[slot] = offCommand;
}
public void onButtonDown(int slot) {
onCommands[slot].execute();
lastCommand = onCommands[slot];
}
public void offButtonDown(int slot) {
offCommands[slot].execute();
lastCommand = offCommands[slot];
}
public void undoButtonDown() {
lastCommand.undo();
}
}
我們看到FanHighCommand和FanOffCommand中有重復(fù)的undo，很容易想到，把它們給“抽象工廠”了：
package javaapplication30;
public class Main {
public static void main(String[] args) {
Light light = new Light();
GarageDoor garageDoor = new GarageDoor();
RemoteControl rc = new RemoteControl();
Command onCommand = new LightOnCommand(light);
Command offCommand = new LightOffCommand(light);
rc.setControl(0, onCommand, offCommand);
onCommand = new GarageDoorOpenCommand(garageDoor);
offCommand = new GarageDoorCloseCommand(garageDoor);
rc.setControl(1, onCommand, offCommand);
rc.onButtonDown(0);
rc.undoButtonDown();
rc.offButtonDown(1);
rc.offButtonDown(0);
rc.onButtonDown(1);
rc.undoButtonDown();
Fan fan = new Fan();
onCommand = new FanHighCommand(fan);
offCommand = new FanOffCommand(fan);
rc.setControl(2, onCommand, offCommand);
rc.onButtonDown(2);
rc.offButtonDown(2);
rc.undoButtonDown();
}
}
class Light {
public void on() {
System.out.println("turn Light on.");
}
void off() {
System.out.println("turn light off");
}
}
class GarageDoor {
public void open() {
System.out.println("open GarageDoor");
}
public void close() {
System.out.println("close GarageDoor");
}
}
class Fan {
public final int HIGH = 3;
public final int MEDIUM = 2;
public final int LOW = 1;
public final int OFF = 0;
public int speed = 0;
public void high() {
speed = HIGH;
System.out.println("Fan's speed is " + speed);
}
public void low() {
speed = LOW;
System.out.println("Fan's speed is " + speed);
}
public void medium() {
speed = MEDIUM;
System.out.println("Fan's speed is " + speed);
}
public void off() {
speed = OFF;
System.out.println("Fan's speed is " + speed);
}
public int getSpeed() {
return speed;
}
}
interface Command {
public void execute();
public void undo();
}
class noCommand implements Command {
public void execute() {
System.out.println("no command here.");
}
public void undo() {
System.out.println("no command here.");
}
}
abstract class FanCommand {
Fan fan;
int preSpeed;
abstract void execute();
public void undo() {
if (preSpeed == fan.HIGH) {
fan.high();
}
else if (preSpeed == fan.MEDIUM) {
fan.medium();
}
else if (preSpeed == fan.LOW) {
fan.low();
}
else if (preSpeed == fan.OFF) {
fan.off();
}
}
}
class FanHighCommand extends FanCommand implements Command {
FanHighCommand(Fan fan) {
super.fan = fan;
}
public void execute() {
preSpeed = fan.getSpeed();
fan.high();
}
}
class FanOffCommand extends FanCommand implements Command {
FanOffCommand(Fan fan) {
super.fan = fan;
}
public void execute() {
preSpeed = fan.getSpeed();
fan.off();
}
}
class LightOnCommand implements Command {
Light light;
LightOnCommand(Light light) {
this.light = light;
}
public void execute() {
light.on();
}
public void undo() {
light.off();
}
}
class LightOffCommand implements Command {
Light light;
LightOffCommand(Light light) {
this.light = light;
}
public void execute() {
light.off();
}
public void undo() {
light.on();
}
}
class GarageDoorOpenCommand implements Command {
GarageDoor garageDoor;
GarageDoorOpenCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.open();
}
public void undo() {
garageDoor.close();
}
}
class GarageDoorCloseCommand implements Command {
GarageDoor garageDoor;
GarageDoorCloseCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.close();
}
public void undo() {
garageDoor.open();
}
}
class RemoteControl {
Command[] onCommands;
Command[] offCommands;
Command noCommand = new noCommand();
Command lastCommand;
public RemoteControl() {
onCommands = new Command[7];
offCommands = new Command[7];
for (int i = 0; i < 7; i++) {
onCommands[i] = noCommand;
offCommands[i] = noCommand;
}
}
public void setControl(int slot, Command onCommand, Command offCommand) {
onCommands[slot] = onCommand;
offCommands[slot] = offCommand;
}
public void onButtonDown(int slot) {
onCommands[slot].execute();
lastCommand = onCommands[slot];
}
public void offButtonDown(int slot) {
offCommands[slot].execute();
lastCommand = offCommands[slot];
}
public void undoButtonDown() {
lastCommand.undo();
}
}
下面我們想讓一個(gè)按鈕實(shí)現(xiàn)一串命令：關(guān)燈，關(guān)電扇，開車庫(kù)。很顯然，用一個(gè)新的XXXCommand實(shí)現(xiàn)即可。
package javaapplication30;
public class Main {
public static void main(String[] args) {
Light light = new Light();
GarageDoor garageDoor = new GarageDoor();
RemoteControl rc = new RemoteControl();
Command onCommand = new LightOnCommand(light);
Command offCommand = new LightOffCommand(light);
rc.setControl(0, onCommand, offCommand);
onCommand = new GarageDoorOpenCommand(garageDoor);
offCommand = new GarageDoorCloseCommand(garageDoor);
rc.setControl(1, onCommand, offCommand);
rc.onButtonDown(0);
rc.undoButtonDown();
rc.offButtonDown(1);
rc.offButtonDown(0);
rc.onButtonDown(1);
rc.undoButtonDown();
Fan fan = new Fan();
onCommand = new FanHighCommand(fan);
offCommand = new FanOffCommand(fan);
rc.setControl(2, onCommand, offCommand);
rc.onButtonDown(2);
rc.offButtonDown(2);
rc.undoButtonDown();
onCommand = new ConsecutiveCommands(light, garageDoor, fan);
rc.setControl(3, onCommand, null);
rc.onButtonDown(3);
rc.undoButtonDown();
}
}
class Light {
public void on() {
System.out.println("turn Light on.");
}
void off() {
System.out.println("turn light off");
}
}
class GarageDoor {
public void open() {
System.out.println("open GarageDoor");
}
public void close() {
System.out.println("close GarageDoor");
}
}
class Fan {
public final int HIGH = 3;
public final int MEDIUM = 2;
public final int LOW = 1;
public final int OFF = 0;
public int speed = 0;
public void high() {
speed = HIGH;
System.out.println("Fan's speed is " + speed);
}
public void low() {
speed = LOW;
System.out.println("Fan's speed is " + speed);
}
public void medium() {
speed = MEDIUM;
System.out.println("Fan's speed is " + speed);
}
public void off() {
speed = OFF;
System.out.println("Fan's speed is " + speed);
}
public int getSpeed() {
return speed;
}
}
interface Command {
public void execute();
public void undo();
}
class noCommand implements Command {
public void execute() {
System.out.println("no command here.");
}
public void undo() {
System.out.println("no command here.");
}
}
abstract class FanCommand {
Fan fan;
int preSpeed;
abstract void execute();
public void undo() {
if (preSpeed == fan.HIGH) {
fan.high();
}
else if (preSpeed == fan.MEDIUM) {
fan.medium();
}
else if (preSpeed == fan.LOW) {
fan.low();
}
else if (preSpeed == fan.OFF) {
fan.off();
}
}
}
class FanHighCommand extends FanCommand implements Command {
FanHighCommand(Fan fan) {
super.fan = fan;
}
public void execute() {
preSpeed = fan.getSpeed();
fan.high();
}
}
class FanOffCommand extends FanCommand implements Command {
FanOffCommand(Fan fan) {
super.fan = fan;
}
public void execute() {
preSpeed = fan.getSpeed();
fan.off();
}
}
class ConsecutiveCommands implements Command {
Light light;
Fan fan;
GarageDoor garageDoor;
int preSpeed;
ConsecutiveCommands(Light light, GarageDoor garageDoor, Fan fan) {
this.light = light;
this.garageDoor = garageDoor;
this.fan = fan;
}
public void execute() {
light.off(); //關(guān)燈
preSpeed = fan.getSpeed(); //記錄原先的電扇檔位
fan.off(); //關(guān)電扇
garageDoor.open() ; //開車庫(kù)
}
public void undo() {
light.on();
if (preSpeed == fan.HIGH) {
fan.high();
}
else if (preSpeed == fan.MEDIUM) {
fan.medium();
}
else if (preSpeed == fan.LOW) {
fan.low();
}
else if (preSpeed == fan.OFF) {
fan.off();
}
garageDoor.close();
}
}
class LightOnCommand implements Command {
Light light;
LightOnCommand(Light light) {
this.light = light;
}
public void execute() {
light.on();
}
public void undo() {
light.off();
}
}
class LightOffCommand implements Command {
Light light;
LightOffCommand(Light light) {
this.light = light;
}
public void execute() {
light.off();
}
public void undo() {
light.on();
}
}
class GarageDoorOpenCommand implements Command {
GarageDoor garageDoor;
GarageDoorOpenCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.open();
}
public void undo() {
garageDoor.close();
}
}
class GarageDoorCloseCommand implements Command {
GarageDoor garageDoor;
GarageDoorCloseCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.close();
}
public void undo() {
garageDoor.open();
}
}
class RemoteControl {
Command[] onCommands;
Command[] offCommands;
Command noCommand = new noCommand();
Command lastCommand;
public RemoteControl() {
onCommands = new Command[7];
offCommands = new Command[7];
for (int i = 0; i < 7; i++) {
onCommands[i] = noCommand;
offCommands[i] = noCommand;
}
}
public void setControl(int slot, Command onCommand, Command offCommand) {
onCommands[slot] = onCommand;
offCommands[slot] = offCommand;
}
public void onButtonDown(int slot) {
onCommands[slot].execute();
lastCommand = onCommands[slot];
}
public void offButtonDown(int slot) {
offCommands[slot].execute();
lastCommand = offCommands[slot];
}
public void undoButtonDown() {
lastCommand.undo();
}
}
這里有個(gè)問題，就是ConsecutiveCommand給寫死了，如果我還需要一個(gè)新的連續(xù)的命令組合，我就要編寫ConsecutiveCommand2，ConsecutiveCommand3等等。能不能只寫一個(gè)，而實(shí)現(xiàn)動(dòng)態(tài)配置呢？靠傳個(gè)參數(shù)告訴它要執(zhí)行哪一串命令可以嗎？
package javaapplication30;
public class Main {
public static void main(String[] args) {
Light light = new Light();
GarageDoor garageDoor = new GarageDoor();
Fan fan = new Fan();
RemoteControl rc = new RemoteControl();
Command fanHighCommand = new FanHighCommand(fan);
Command fanOffCommand = new FanOffCommand(fan);
Command garageDoorCloseCommand = new GarageDoorCloseCommand(garageDoor);
Command garageDoorOpenCommand = new GarageDoorOpenCommand(garageDoor);
Command lightOffCommand = new LightOffCommand(light);
Command lightOnCommand = new LightOnCommand(light);
Command[] commands = {lightOffCommand, fanOffCommand, garageDoorOpenCommand};
Command consecutiveCommands = new ConsecutiveCommands(commands);
rc.setControl(0, fanHighCommand, fanOffCommand);
rc.setControl(1, garageDoorOpenCommand, garageDoorCloseCommand);
rc.setControl(2, lightOnCommand, lightOffCommand);
rc.setControl(3, consecutiveCommands, null);
for(int i=0;i<=3;i++)
rc.onButtonDown(i);
}
}
class Light {
public void on() {
System.out.println("turn Light on.");
}
void off() {
System.out.println("turn light off");
}
}
class GarageDoor {
public void open() {
System.out.println("open GarageDoor");
}
public void close() {
System.out.println("close GarageDoor");
}
}
class Fan {
public final int HIGH = 3;
public final int MEDIUM = 2;
public final int LOW = 1;
public final int OFF = 0;
public int speed = 0;
public void high() {
speed = HIGH;
System.out.println("Fan's speed is " + speed);
}
public void low() {
speed = LOW;
System.out.println("Fan's speed is " + speed);
}
public void medium() {
speed = MEDIUM;
System.out.println("Fan's speed is " + speed);
}
public void off() {
speed = OFF;
System.out.println("Fan's speed is " + speed);
}
public int getSpeed() {
return speed;
}
}
interface Command {
public void execute();
public void undo();
}
class noCommand implements Command {
public void execute() {
System.out.println("no command here.");
}
public void undo() {
System.out.println("no command here.");
}
}
abstract class FanCommand {
Fan fan;
int preSpeed;
abstract void execute();
public void undo() {
if (preSpeed == fan.HIGH) {
fan.high();
}
else if (preSpeed == fan.MEDIUM) {
fan.medium();
}
else if (preSpeed == fan.LOW) {
fan.low();
}
else if (preSpeed == fan.OFF) {
fan.off();
}
}
}
class FanHighCommand extends FanCommand implements Command {
FanHighCommand(Fan fan) {
super.fan = fan;
}
public void execute() {
preSpeed = fan.getSpeed();
fan.high();
}
}
class FanOffCommand extends FanCommand implements Command {
FanOffCommand(Fan fan) {
super.fan = fan;
}
public void execute() {
preSpeed = fan.getSpeed();
fan.off();
}
}
class ConsecutiveCommands implements Command {
Command[] commands;
ConsecutiveCommands(Command[] commands) {
this.commands = commands;
}
public void execute() {
for (int i = 0; i < commands.length; i++) {
commands[i].execute();
}
}
public void undo() {
for (int i = 0; i < commands.length; i++) {
commands[i].undo();
}
}
}
class LightOnCommand implements Command {
Light light;
LightOnCommand(Light light) {
this.light = light;
}
public void execute() {
light.on();
}
public void undo() {
light.off();
}
}
class LightOffCommand implements Command {
Light light;
LightOffCommand(Light light) {
this.light = light;
}
public void execute() {
light.off();
}
public void undo() {
light.on();
}
}
class GarageDoorOpenCommand implements Command {
GarageDoor garageDoor;
GarageDoorOpenCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.open();
}
public void undo() {
garageDoor.close();
}
}
class GarageDoorCloseCommand implements Command {
GarageDoor garageDoor;
GarageDoorCloseCommand(GarageDoor garageDoor) {
this.garageDoor = garageDoor;
}
public void execute() {
garageDoor.close();
}
public void undo() {
garageDoor.open();
}
}
class RemoteControl {
Command[] onCommands;
Command[] offCommands;
Command noCommand = new noCommand();
Command lastCommand;
public RemoteControl() {
onCommands = new Command[7];
offCommands = new Command[7];
for (int i = 0; i < 7; i++) {
onCommands[i] = noCommand;
offCommands[i] = noCommand;
}
}
public void setControl(int slot, Command onCommand, Command offCommand) {
onCommands[slot] = onCommand;
offCommands[slot] = offCommand;
}
public void onButtonDown(int slot) {
onCommands[slot].execute();
lastCommand = onCommands[slot];
}
public void offButtonDown(int slot) {
offCommands[slot].execute();
lastCommand = offCommands[slot];
}
public void undoButtonDown() {
lastCommand.undo();
}
}