定義：將“請(qǐng)求”封裝成對(duì)象我抠，以便使用不同的請(qǐng)求糠惫、隊(duì)列或者日志來(lái)參數(shù)化其他對(duì)象榨惠。命令模式也支持撤銷(xiāo)的操作隆判。注意命令模式是將請(qǐng)求封裝成對(duì)象缤至！
其實(shí)簡(jiǎn)單的說(shuō)厉斟，命令模式就是把方法調(diào)用封裝起來(lái)了欧聘，通過(guò)封裝方法調(diào)用捂蕴，可以把運(yùn)算塊包裝成型顽铸，所以調(diào)用此運(yùn)算的對(duì)象不需要關(guān)心事情是如何進(jìn)行的茁计，只要知道如何使用包裝成型的方法來(lái)完成它就可以。
命令模式的使用場(chǎng)景：當(dāng)需要將發(fā)出請(qǐng)求的對(duì)象和執(zhí)行請(qǐng)求的對(duì)象解耦的時(shí)候跋破，請(qǐng)考慮使用命令模式吧簸淀。
場(chǎng)景舉例：設(shè)計(jì)一款多功能遙控器，該遙控器可以控制家里各個(gè)電器的狀態(tài)毒返，例如電燈的開(kāi)關(guān)租幕，電視的開(kāi)關(guān)，電扇的速度拧簸，車(chē)庫(kù)門(mén)的開(kāi)關(guān)等等劲绪，下面使用命令模式實(shí)現(xiàn)這個(gè)遙控器。在這里盆赤，發(fā)出請(qǐng)求的對(duì)象是遙控器贾富，執(zhí)行請(qǐng)求的對(duì)象是各種電器。
首先需要讓所有的命令對(duì)象實(shí)現(xiàn)同一個(gè)命令接口
public interface Command {
public void execute();
public void undo();
}
接口中有兩個(gè)方法牺六，一個(gè)是執(zhí)行動(dòng)作的方法execute颤枪，一個(gè)是撤銷(xiāo)動(dòng)作的方法undo；
下面實(shí)現(xiàn)電燈打開(kāi)關(guān)閉命令前先聲明一個(gè)電燈類(lèi)
public class Light {
protected void on() {
System.out.println("light is on");
}
protected void off() {
System.out.println("light is off");
}
}
電燈類(lèi)只有兩個(gè)方法on—>打開(kāi)淑际，off—>關(guān)閉畏纲；然后實(shí)現(xiàn)打開(kāi)電燈的命令
public class LightOnCommand implements Command {
Light light;
public LightOnCommand(Light light) {
// TODO Auto-generated constructor stub
this.light = light;
}
@Override
public void execute() {
// TODO Auto-generated method stub
light.on();
}
@Override
public void undo() {
// TODO Auto-generated method stub
light.off();
}
}
注意undo的操作正好是與execute的操作相反的扇住；在寫(xiě)一個(gè)電燈關(guān)閉的命令。
public class LightOffCommand implements Command {
Light light;
public LightOffCommand(Light light) {
// TODO Auto-generated constructor stub
this.light = light;
}
@Override
public void execute() {
// TODO Auto-generated method stub
light.off();
}
@Override
public void undo() {
// TODO Auto-generated method stub
light.on();
}
}
再增加一個(gè)車(chē)庫(kù)門(mén)的開(kāi)啟和關(guān)閉盗胀。
public class GarageDoor {
public void up() {
System.out.println("the garagedoor is up!");
}
public void down() {
System.out.println("the garagedoor is down!");
}
public void lightOn() {
System.out.println("the garagedoor's light is on!");
}
public void lightOff() {
System.out.println("the garagedoor's light is off!");
}
}
public class GarageDoorOpenCommand implements Command {
GarageDoor garageDoor;
public GarageDoorOpenCommand(GarageDoor garageDoor) {
// TODO Auto-generated constructor stub
this.garageDoor = garageDoor;
}
@Override
public void execute() {
// TODO Auto-generated method stub
garageDoor.up();
garageDoor.lightOn();
}
@Override
public void undo() {
// TODO Auto-generated method stub
garageDoor.down();
garageDoor.lightOff();
}
}
public class GarageDoorCloseCommand implements Command {
GarageDoor garageDoor;
public GarageDoorCloseCommand(GarageDoor garageDoor) {
// TODO Auto-generated constructor stub
this.garageDoor = garageDoor;
}
@Override
public void execute() {
// TODO Auto-generated method stub
garageDoor.down();
garageDoor.lightOff();
}
@Override
public void undo() {
// TODO Auto-generated method stub
garageDoor.up();
garageDoor.lightOn();
}
}
然后就是遙控器的實(shí)現(xiàn)了艘蹋。
public class RemoteControl {
/*
* 由于對(duì)應(yīng)多個(gè)電器這里采用數(shù)組記錄這些命令
*/
Command[] onCommands;
Command[] offCommands;
Command undoCommand;//用來(lái)記錄撤銷(xiāo)命令
public RemoteControl() {
// TODO Auto-generated constructor stub
onCommands = new Command[7];
offCommands = new Command[7];
Command noCommand = new NoCommand();//初始化是都是空命令
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();
}
}
空命令在這里什么也不做，只是保證上的按鈕均有命令對(duì)象存在票灰，空命令的實(shí)現(xiàn)女阀。
public class NoCommand implements Command {
@Override
public void execute() {
// TODO Auto-generated method stub
System.out.println("no command!");
}
@Override
public void undo() {
// TODO Auto-generated method stub
}
}
開(kāi)始測(cè)試一下遙控器。
public class RemoteLoader {
public static void main(String[] args) {
// TODO Auto-generated method stub
RemoteControl remoteControl=new RemoteControl();
Light light=new Light();
LightOnCommand lightOn=new LightOnCommand(light);
LightOffCommand lightOff =new LightOffCommand(light);
GarageDoor garageDoor=new GarageDoor();
GarageDoorOpenCommand garageDoorOpen=new GarageDoorOpenCommand(garageDoor);
GarageDoorCloseCommand garageDoorClose=new GarageDoorCloseCommand(garageDoor);
remoteControl.setCommand(0, lightOn, lightOff);
remoteControl.setCommand(1, garageDoorOpen, garageDoorClose);
remoteControl.onButtonWasPushed(0);
remoteControl.onButtonWasPushed(1);
remoteControl.offButtonWasPushed(0);
remoteControl.offButtonWasPushed(1);
}
}
打印結(jié)果：
light is on
the garagedoor is up!
the garagedoor's light is on!
light is off
the garagedoor is down!
the garagedoor's light is off!
遙控器實(shí)現(xiàn)完畢屑迂，測(cè)試一下撤銷(xiāo)命令浸策。
public class RemoteLoader {
public static void main(String[] args) {
// TODO Auto-generated method stub
RemoteControl remoteControl=new RemoteControl();
Light light=new Light();
LightOnCommand lightOn=new LightOnCommand(light);
LightOffCommand lightOff =new LightOffCommand(light);
remoteControl.setCommand(0, lightOn, lightOff);
remoteControl.onButtonWasPushed(0);
System.out.println("****************");
remoteControl.undoButtonWasPushed();
}
}
打印結(jié)果：
light is on
****************
light is off
**總結(jié) **：
（1）命令模式將發(fā)出請(qǐng)求的對(duì)象和執(zhí)行請(qǐng)求的對(duì)象解耦屈糊；
〉拈弧（2）在被解耦的兩者之間是通過(guò)命令對(duì)象進(jìn)行溝通的。命令對(duì)象封裝了接受者和一個(gè)或一組動(dòng)作逻锐。
》蛏巍（3）調(diào)用者通過(guò)調(diào)用命令對(duì)象的execute（）發(fā)出請(qǐng)求，這會(huì)使得接受者的動(dòng)作被調(diào)用昧诱。
∠怼（4）調(diào)用者可以接受命令當(dāng)作參數(shù)，甚至在運(yùn)行時(shí)動(dòng)態(tài)的進(jìn)行盏档。
⌒钻（5）命令可以支持撤銷(xiāo)，做法是實(shí)現(xiàn)一個(gè)undo（）方法來(lái)回到上一個(gè)execute（）被執(zhí)行前的狀態(tài)蜈亩。
