行为模式：Command（命令）

/* The Command interface */
public interface Command {
void execute();
}

import java.util.List;
import java.util.ArrayList;

/* The Invoker class */
public class Switch {
private List<Command> history = new ArrayList<Command>();

public Switch() {
}

public void storeAndExecute(Command cmd) {
this.history.add(cmd); // optional
cmd.execute();
}
}

/* The 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 for turning on the light - ConcreteCommand #1 */
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 - ConcreteCommand #2 */
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);

Switch s = new Switch();

try {
if (args[0].equalsIgnoreCase("ON")) {
s.storeAndExecute(switchUp);
}
else if (args[0].equalsIgnoreCase("OFF")) {
s.storeAndExecute(switchDown);
}
else {
System.out.println("Argument \"ON\" or \"OFF\" is required.");
}
} catch (Exception e) {
System.out.println("Arguments required.");
}
}
}