设计模式-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。支持可撤销操作。
命令可以将不同运算块打包，许久之后，运算依然可以被调用。衍生一些应用，如：Scheduler、线程池、工作队列等。
日志请求：将动命令作记录到日志中，系统死机后可以通过重新调用这些动作恢复到之前的状态。

主要解决：在软件系统中，行为请求者与行为实现者通常是一种紧耦合的关系，但某些场合，比如需要对行为进行记录、撤销或重做、事务等处理时，这种无法抵御变化的紧耦合的设计就不太合适。
何时使用：在某些场合，比如要对行为进行”记录、撤销/重做、事务”等处理，这种无法抵御变化的紧耦合是不合适的。在这种情况下，如何将”行为请求者”与”行为实现者”解耦？将一组行为抽象为对象，可

优点： 1、降低了系统耦合度。 2、新的命令可以很容易添加到系统中去。
缺点：使用命令模式可能会导致某些系统有过多的具体命令类。

家电遥控器举例：

public class Light {    String name;    public Light() {        this.name = "Light";    }    public Light(String name) {        super();        this.name = name;    }    public void on() {        System.out.println(name + " is oning");    }    public void off() {        System.out.println(name + " is off");    }}public class GarageDoor {    String name;    public GarageDoor() {        this.name = "Garage Door";    }    public GarageDoor(String name) {        super();        this.name = name;    }    public void open() {        System.out.println("Garage Door is Open");    }    public void close() {        System.out.println("Garage Door is close");    }}public interface Command {    public void execute();    public void undo();}public class LightOnCommand implements Command {    Light light;    public LightOnCommand(Light light) {        super();        this.light = light;    }    @Override    public void execute() {        light.on();    }    @Override    public void undo() {        light.off();    }}public class LightOffCommand implements Command {    Light light;    public LightOffCommand(Light light) {        super();        this.light = light;    }    @Override    public void execute() {        light.off();    }    @Override    public void undo() {        light.on();    }}public class GarageDoorOpenCommand implements Command {    GarageDoor door;    public GarageDoorOpenCommand(GarageDoor door) {        this.door = door;    }    @Override    public void execute() {        door.open();    }    @Override    public void undo() {        door.close();    }}public class GarageDoorCloseCommand implements Command {    GarageDoor door;    public GarageDoorCloseCommand(GarageDoor door) {        this.door = door;    }    @Override    public void execute() {        door.close();    }    @Override    public void undo() {        door.open();    }}//控制多个开关命令public class MacroCommand implements Command {    Command[] commands;    public MacroCommand(Command[] commands) {        this.commands = commands;    }    @Override    public void execute() {        for(Command command: commands){            command.execute();        }    }    @Override    public void undo() {        for(Command command: commands){            command.undo();        }    }}public class NoCommand implements Command {    @Override    public void execute() {    }    @Override    public void undo() {    }}public class SimpleRemoteControl {    Command slot;    public void setCommand(Command slot) {        this.slot = slot;    }    public void buttonWasPressed(){        slot.execute();    }}/** * 遥控器 */public class RemoteControl {    Command[] onCommands;    Command[] offCommands;    Command undoCommand;    public RemoteControl(){        onCommands = new Command[7];        offCommands = new Command[7];        Command noCommand = new NoCommand();        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 onButtonWasPress(int slot){        onCommands[slot].execute();        undoCommand = onCommands[slot];    }    public void offButtonWasPress(int slot){        offCommands[slot].execute();        undoCommand = offCommands[slot];    }    public void undoButtonWasPushed(){        undoCommand.undo();    }    @Override    public String toString(){        StringBuffer buffer = new StringBuffer();        buffer.append("\n-----romote Control---------\n");        for(int i=0; i<onCommands.length; i++){            buffer.append("[slot " + i + "] " + onCommands[i].getClass().getName()                    + "   " + offCommands[i].getClass().getName() + "\n");        }        return buffer.toString();    }}public class RemoteControlTest {    public static void main(String[] args) {        SimpleRemoteControl remote = new SimpleRemoteControl();        Light light = new Light();        LightOnCommand lightOn = new LightOnCommand(light);        remote.setCommand(lightOn);        remote.buttonWasPressed();    }}public class RemoteLoader {    public static void main(String[] args) {        RemoteControl remoteControl = new RemoteControl();        Light livingRoomLight = new Light("Living room light");        Light kitchenLight = new Light("Kitchen light");        GarageDoor garageDoor = new GarageDoor();        LightOnCommand livingRoomLightOn = new LightOnCommand(livingRoomLight);        LightOffCommand livingRoomLightOff = new LightOffCommand(livingRoomLight);        LightOnCommand kitchenLightOn = new LightOnCommand(kitchenLight);        LightOffCommand kitchenLightOff = new LightOffCommand(kitchenLight);        GarageDoorOpenCommand garageDoorOpen = new GarageDoorOpenCommand(garageDoor);        GarageDoorCloseCommand garageDoorclose = new GarageDoorCloseCommand(garageDoor);        Command[] partyOn = {livingRoomLightOn, kitchenLightOn, garageDoorOpen};        Command[] partyOff = {livingRoomLightOff, kitchenLightOff, garageDoorclose};        //总控开启所有电器        MacroCommand partyOnMacro = new MacroCommand(partyOn);        //总控关闭所有电器        MacroCommand partyOffMacro = new MacroCommand(partyOff);        remoteControl.setCommand(0, livingRoomLightOn, livingRoomLightOff);        remoteControl.setCommand(1, kitchenLightOn, kitchenLightOff);        remoteControl.setCommand(2, garageDoorOpen, garageDoorclose);        remoteControl.setCommand(6, partyOnMacro, partyOffMacro);        System.out.println(remoteControl);        remoteControl.onButtonWasPress(0);        remoteControl.offButtonWasPress(0);        remoteControl.onButtonWasPress(1);        remoteControl.offButtonWasPress(1);        remoteControl.onButtonWasPress(2);        remoteControl.offButtonWasPress(2);        remoteControl.undoButtonWasPushed();        System.out.println("\n=========open all=========");        remoteControl.onButtonWasPress(6);        System.out.println("\n=========close all=========");        remoteControl.offButtonWasPress(6);        System.out.println("\n=========undo all=========");        remoteControl.undoButtonWasPushed();    }}