《設計模式》之命令模式

時間 2019-12-25

標籤設計模式命令模式简体版

原文原文鏈接

1、命令模式定義

命令你們都不會陌生，那麼在開始命令模式以前，能夠想象一下生活中的命令模式的特色：app

如老闆命令你完成一個OA項目是一個命令，接着看看其特色：eclipse

一、在上面的命令中，命令的執行者確定是聰明的你了。具體的執行方法，多是經過vs實現，或者是經過eclipse實現,由此看來：命令要有個命令的執行者，還要有個命令的執行方法。測試

二、命令的發出者很明顯是老闆，老闆還有個發出方法，多是經過電話給你說，也可能給你郵件給你說，也多是經過開會給你說。因此命令的發出者要有一個命令，還要有個發出的方法。this

三、最後看看命令，命令有個名字，命令的確定要執行。並且命令是在boss給你發出通知後執行的。spa

接下來看看命令模式的定義：日誌

命令模式：將請求封裝成對象，以便使用不一樣的請求、日誌、隊列等來參數化其餘對象。命令模式也支持撤銷操做。對象

2、問題描述

使用命令模式實現遙控器，遙控器上的不一樣按鈕控制電燈的開關及亮度、天花板風扇的開關及轉速等，支持撤銷。具體按鈕：開燈/關燈按鈕、暗光開/關按鈕、風扇高速/中速/低速/關按鈕、撤銷按鈕。遙控器以下圖所示：隊列

遙控器擔當請求者（或稱爲調用者）的角色，用RemoteControlWithUndo類實現，其內有Command[]類型的屬性onCommands和offCommands表示對應的一組開關，Command類型的屬性undoCommand記錄最後執行的命令用於命令的撤銷。遙控器上有7組開關按鈕和一個撤銷按鈕。每一個按鈕對應一個具體命令，說明以下：ip

3、類圖

4、代碼實現

1.命令角色：Command

public interface Command {
public void execute();
public void undo();//實現撤銷
}

2.接收者角色：Light、CeilingFan

(1)Light電燈：rem

public class Light {
String location;
int level;//燈光的亮度
public Light(String location) {
this.location = location;
}
public void on() {
level = 100;
System.out.println("Light is on");
}
public void off() {
level = 0;
System.out.println("Light is off");
}
//調整燈光的亮度
public void dim(int level) {
this.level = level;
if (level == 0) {
off();
}
else {
System.out.println("Light is dimmed to " + level + "%");
}
}
//獲取燈光的亮度
public int getLevel() {
return level;
}
}

(2)CeilingFan風扇：

public class CeilingFan {
public static final int HIGH = 3;
public static final int MEDIUM = 2;
public static final int LOW = 1;
public static final int OFF = 0;
String location;//例如臥室、客廳的風扇？
int speed;
public CeilingFan(String location) {
this.location = location;
speed = OFF;
}
public void high() {
speed = HIGH;
System.out.println(location + " ceiling fan is on high");
}
public void medium() {
speed = MEDIUM;
System.out.println(location + " ceiling fan is on medium");
}
public void low() {
speed = LOW;
System.out.println(location + " ceiling fan is on low");
}
public void off() {
speed = OFF;
System.out.println(location + " ceiling fan is off");
}
public int getSpeed() {
return speed;
}
}

3.具體命令角色：各類命令

(1)NoCommand：空命令，建立遙控器時默認其持有的都是空命令（相比判斷null更好），什麼事也不作

public class NoCommand implements Command {
public void execute() { }
public void undo() { }
}

(2)LightOnCommand：開燈命令

public class LightOnCommand implements Command {
Light light;
int level;//level用於記錄上次的燈光亮度
public LightOnCommand(Light light) {
this.light = light;
}
public void execute() {
level = light.getLevel();
light.on();
}
public void undo() {//將燈光的亮度調到前一次的水平實現撤銷
light.dim(level);
}
}

(3)LightOffCommand：關燈命令

public class LightOffCommand implements Command {
Light light;
int level;
public LightOffCommand(Light light) {
this.light = light;
}
public void execute() {
level = light.getLevel();
light.off();
}
public void undo() {
light.dim(level);
}
}

(4)DimmerLightOnCommand：開啓暗光

public class DimmerLightOnCommand implements Command {
Light light;
int prevLevel;//記錄之前的燈光亮度，撤銷操做時使用
public DimmerLightOnCommand(Light light) {
this.light = light;
}
public void execute() {
prevLevel = light.getLevel();
light.dim(75);//將燈光亮度調至75%實現暗光
}
public void undo() {
light.dim(prevLevel);
}
}

(5)DimmerLightOffCommand：關閉暗光

public class DimmerLightOffCommand implements Command {
Light light;
int prevLevel;
public DimmerLightOffCommand(Light light) {
this.light = light;
prevLevel = 100;
}
public void execute() {
prevLevel = light.getLevel();
light.off();
}
public void undo() {
light.dim(prevLevel);
}
}

(6)CeilingFanHighCommand：風扇高轉速

public class CeilingFanHighCommand implements Command {
CeilingFan ceilingFan;
int prevSpeed;//記錄之前的轉速，用於撤銷操做（0時表示之前的狀態是：關）
public CeilingFanHighCommand(CeilingFan ceilingFan) {
this.ceilingFan = ceilingFan;
}
public void execute() {
prevSpeed = ceilingFan.getSpeed();
ceilingFan.high();
}
public void undo() {
if (prevSpeed == CeilingFan.HIGH) {
ceilingFan.high();
} else if (prevSpeed == CeilingFan.MEDIUM) {
ceilingFan.medium();
} else if (prevSpeed == CeilingFan.LOW) {
ceilingFan.low();
} else if (prevSpeed == CeilingFan.OFF) {
ceilingFan.off();
}
}
}

(7)CeilingFanMediumCommand：風扇中轉速

public class CeilingFanMediumCommand implements Command {
CeilingFan ceilingFan;
int prevSpeed;
public CeilingFanMediumCommand(CeilingFan ceilingFan) {
this.ceilingFan = ceilingFan;
}
public void execute() {
prevSpeed = ceilingFan.getSpeed();
ceilingFan.medium();//將行爲的真正執行委託給接收者，此處即ceilingFan風扇對象
}
public void undo() {
if (prevSpeed == CeilingFan.HIGH) {
ceilingFan.high();
} else if (prevSpeed == CeilingFan.MEDIUM) {
ceilingFan.medium();
} else if (prevSpeed == CeilingFan.LOW) {
ceilingFan.low();
} else if (prevSpeed == CeilingFan.OFF) {
ceilingFan.off();
}
}
}

(8)CeilingFanLowCommand：風扇低轉速

public class CeilingFanLowCommand implements Command {
CeilingFan ceilingFan;
int prevSpeed;
public CeilingFanLowCommand(CeilingFan ceilingFan) {
this.ceilingFan = ceilingFan;
}
public void execute() {
prevSpeed = ceilingFan.getSpeed();
ceilingFan.low();
}
public void undo() {
if (prevSpeed == CeilingFan.HIGH) {
ceilingFan.high();
} else if (prevSpeed == CeilingFan.MEDIUM) {
ceilingFan.medium();
} else if (prevSpeed == CeilingFan.LOW) {
ceilingFan.low();
} else if (prevSpeed == CeilingFan.OFF) {
ceilingFan.off();
}
}
}

(9)CeilingFanOffCommand：關閉風扇

public class CeilingFanOffCommand implements Command {
CeilingFan ceilingFan;
int prevSpeed;
public CeilingFanOffCommand(CeilingFan ceilingFan) {
this.ceilingFan = ceilingFan;
}
public void execute() {
prevSpeed = ceilingFan.getSpeed();
ceilingFan.off();
}
public void undo() {
if (prevSpeed == CeilingFan.HIGH) {
ceilingFan.high();
} else if (prevSpeed == CeilingFan.MEDIUM) {
ceilingFan.medium();
} else if (prevSpeed == CeilingFan.LOW) {
ceilingFan.low();
} else if (prevSpeed == CeilingFan.OFF) {
ceilingFan.off();
}
}
}

4.遙控器類，請求者（或調用者）角色，持有多個Command對象

public class RemoteControlWithUndo {
Command[] onCommands;//對應多個開按鈕
Command[] offCommands;//對應多個關按鈕
Command undoCommand;//對應撤銷按鈕
public RemoteControlWithUndo() {
onCommands = new Command[7];
offCommands = new Command[7];
Command noCommand = new NoCommand();
for(int i=0;i<7;i++) {
onCommands[i] = noCommand;//默認賦值爲空命令，什麼事也不作
offCommands[i] = noCommand;
}
undoCommand = noCommand;
}
public void setCommand(int slot, Command onCommand, Command offCommand) {
onCommands[slot] = onCommand;
offCommands[slot] = offCommand;
}
//當編號爲第slot的開On按鈕按下時執行命令
public void onButtonWasPushed(int slot) {
onCommands[slot].execute();
undoCommand = onCommands[slot];//記錄最後執行的命令
}
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 Control -------\n");
for (int i = 0; i < onCommands.length; i++) {
stringBuff.append("[slot " + i + "] " + onCommands[i].getClass().getName()
+ " " + offCommands[i].getClass().getName() + "\n");
}
stringBuff.append("[undo] " + undoCommand.getClass().getName() + "\n");
return stringBuff.toString();
}
}

5.測試

public class RemoteLoader {
public static void main(String[] args) {
RemoteControlWithUndo remoteControl = new RemoteControlWithUndo();
Light livingRoomLight = new Light("Living Room");
LightOnCommand livingRoomLightOn = new LightOnCommand(livingRoomLight);
LightOffCommand livingRoomLightOff = new LightOffCommand(livingRoomLight);
DimmerLightOnCommand dimmerLightOnCommand=new DimmerLightOnCommand(livingRoomLight);
DimmerLightOffCommand dimmerLightOffCommand=new DimmerLightOffCommand(livingRoomLight);
CeilingFan ceilingFan = new CeilingFan("Living Room");
CeilingFanHighCommand ceilingFanHigh = new CeilingFanHighCommand(ceilingFan);
CeilingFanMediumCommand ceilingFanMedium = new CeilingFanMediumCommand(ceilingFan);
CeilingFanLowCommand ceilingFanLow =new CeilingFanLowCommand(ceilingFan);
CeilingFanOffCommand ceilingFanOff = new CeilingFanOffCommand(ceilingFan);
remoteControl.setCommand(0, livingRoomLightOn, livingRoomLightOff);
remoteControl.setCommand(1, dimmerLightOnCommand, dimmerLightOffCommand);
remoteControl.setCommand(2, ceilingFanHigh, ceilingFanOff);
remoteControl.setCommand(3, ceilingFanMedium, ceilingFanOff);
remoteControl.setCommand(4, ceilingFanLow, ceilingFanOff);
remoteControl.onButtonWasPushed(1);
remoteControl.onButtonWasPushed(3);
remoteControl.onButtonWasPushed(2);
remoteControl.offButtonWasPushed(3);
remoteControl.undoButtonWasPushed();
}
}