人在江湖

參考 http://en.wikipedia.org/wiki/Command_pattern

/*the Invoker class*/
public class Switch {
 
    private Command flipUpCommand;
    private Command flipDownCommand;
 
    public Switch(Command flipUpCmd, Command flipDownCmd) {
         this.flipUpCommand = flipUpCmd;
         this.flipDownCommand = flipDownCmd;
    }
 
    public void flipUp() {
         flipUpCommand.execute();
    }
 
    public void flipDown() {
         flipDownCommand.execute();
    }
}
 
/*Receiver class*/
public class Light {
 
     public Light() {  }
 
     public void turnOn() {
        System.out.println("The light is on");
     }
 
     public void turnOff() {
        System.out.println("The light is off");
     }
}
 
/*the Command interface*/
public interface Command {
    void execute();
}
 
/*the Command for turning on the light*/
public class FlipUpCommand implements Command {
 
   private Light theLight;
 
   public FlipUpCommand(Light light) {
        this.theLight=light;
   }
 
   public void execute(){
      theLight.turnOn();
   }
}
 
/*the Command for turning off the light*/
public class FlipDownCommand implements Command {
 
   private Light theLight;
 
   public FlipDownCommand(Light light) {
        this.theLight=light;
   }
 
   public void execute() {
      theLight.turnOff();
   }
}
 
/*The test class or client*/
public class PressSwitch {
 
   public static void main(String[] args) {
       Light lamp = new Light();
       Command switchUp = new FlipUpCommand(lamp);
       Command switchDown = new FlipDownCommand(lamp);
 
       // See criticism of this model above:
       // The switch itself should not be aware of lamp details (switchUp, switchDown) 
       // either directly or indirectly
       Switch s = new Switch(switchUp,switchDown);
 
       try {
           if (args[0].equalsIgnoreCase("ON")) {
                s.flipUp();
           } else if (args[0].equalsIgnoreCase("OFF")) {
               s.flipDown();
           } else {
               System.out.println("Argument \"ON\" or \"OFF\" is required.");
           }
       } catch (Exception e){
           System.out.println("Arguments required.");
       }
   }
}
=====================

java tip (http://www.javaworld.com/javaworld/javatips/jw-javatip68.html?page=3) 給了類似的例子，多了Fan作為receiver:

TestCommand.java
class Fan {
        public void startRotate() {
                System.out.println("Fan is rotating");
        }
        public void stopRotate() {
                System.out.println("Fan is not rotating");
        }
}
class Light {
        public void turnOn( ) {
                System.out.println("Light is on ");
        }
        public void turnOff( ) {
                System.out.println("Light is off");
        }
}
class Switch {
        private Command UpCommand, DownCommand;
        public Switch( Command Up, Command Down) {
                UpCommand = Up; // concrete Command registers itself with the invoker
                DownCommand = Down;
        }
        void flipUp( ) { // invoker calls back concrete Command, which executes the Command on the receiver
                        UpCommand . execute ( ) ;                          
        }
        void flipDown( ) {
                        DownCommand . execute ( );
        }
}
class LightOnCommand implements Command {
        private Light myLight;
        public LightOnCommand ( Light L) {
                myLight  =  L;
        }
        public void execute( ) {
                myLight . turnOn( );
        }
}
class LightOffCommand implements Command {
        private Light myLight;
        public LightOffCommand ( Light L) {
                myLight  =  L;
        }
        public void execute( ) {
                myLight . turnOff( );
        }
}
class FanOnCommand implements Command {
        private Fan myFan;
        public FanOnCommand ( Fan F) {
                myFan  =  F;
        }
        public void execute( ) {
                myFan . startRotate( );
        }
}
class FanOffCommand implements Command {
        private Fan myFan;
        public FanOffCommand ( Fan F) {
                myFan  =  F;
        }
        public void execute( ) {
                myFan . stopRotate( );
        }
}
public class TestCommand {
                public static void main(String[] args) {
                        Light  testLight = new Light( );
                        LightOnCommand testLOC = new LightOnCommand(testLight);
                        LightOffCommand testLFC = new LightOffCommand(testLight);
                        Switch testSwitch = new Switch( testLOC,testLFC);      
                        testSwitch.flipUp( );
                        testSwitch.flipDown( );
                        Fan testFan = new Fan( );
                        FanOnCommand foc = new FanOnCommand(testFan);
                        FanOffCommand ffc = new FanOffCommand(testFan);
                        Switch ts = new Switch( foc,ffc);
                        ts.flipUp( );
                        ts.flipDown( );
                }
}              
Command.java
public interface Command {
        public abstract void execute ( );
}