public interface Command {void execute();void undo();
}

public class LightOffCommand implements Command {private Light light = new Light();public LightOffCommand() {this.light = light;}@Overridepublic void execute() {light.off();}@Overridepublic void undo() {light.on();}
}

public class LightOnCommand implements Command {private Light light = new Light();public LightOnCommand() {this.light = light;}@Overridepublic void execute() {light.on();}@Overridepublic void undo() {light.off();}
}

public class Light {public void on() {System.out.println("Light is on");}public void off() {System.out.println("Light is off");}
}

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

public class StereoOffWithCDCommand implements Command {private Stereo stereo = new Stereo();public StereoOffWithCDCommand() {this.stereo = stereo;}@Overridepublic void execute() {stereo.off();}@Overridepublic void undo() {stereo.on();stereo.setCD();stereo.setVolume(11);}
}

public class StereoOnWithCDCommand implements Command {private Stereo stereo = new Stereo();public StereoOnWithCDCommand() {this.stereo = stereo;}@Overridepublic void execute() {stereo.on();stereo.setCD();stereo.setVolume(11);}@Overridepublic void undo() {stereo.off();}
}

public class Stereo {public void on() {System.out.println("Stereo is on");}public void setCD() {System.out.println("CD is set");}public void setVolume(int volume) {System.out.println("Volume is set " + volume);}public void off() {System.out.println("Stereo is off");}
}

public class RemoteControl {private Command[] onCommands;private Command[] offCommands;private Command undoCommand;public RemoteControl() {onCommands = new Command[2];offCommands = new Command[2];Command command = new NoCommand();for (int i = 0; i < 2; i++) {onCommands[i] = command;offCommands[i] = command;}undoCommand = command;}public void setCommand(int slot, Command onCommand, Command offCommand) {onCommands[slot] = onCommand;offCommands[slot] = offCommand;}public void onButtonWasPush(int slot) {onCommands[slot].execute();undoCommand = onCommands[slot];}public void offButtonWasPush(int slot) {offCommands[slot].execute();undoCommand = offCommands[slot];}public void undoButtonWasPushed() {undoCommand.undo();}@Overridepublic String toString() {StringBuffer stringBuffer = new StringBuffer();stringBuffer.append("\n------ Remote Control ------\n");for (int i = 0; i < onCommands.length; i++) {stringBuffer.append("[slot " + i + "] " + onCommands[i].getClass().getName() + "     " + offCommands[i].getClass().getName() + "\n");}return stringBuffer.toString();}
}

public class RemoteControlTest {public static void main(String[] args) {RemoteControl remte = new RemoteControl();LightOnCommand lightOnCommand = new LightOnCommand();LightOffCommand lightOffCommand = new LightOffCommand();StereoOnWithCDCommand onWithCDCommand = new StereoOnWithCDCommand();StereoOffWithCDCommand offWithCDCommand = new StereoOffWithCDCommand();remte.setCommand(0, lightOnCommand, lightOffCommand);remte.setCommand(1, onWithCDCommand, offWithCDCommand);System.out.println(remte.toString());remte.onButtonWasPush(0);remte.onButtonWasPush(1);remte.offButtonWasPush(0);remte.offButtonWasPush(1);remte.undoButtonWasPushed();}
}