patterns14CommandPattern

1package pkg8patterns;2 3/*4 * Command (Behavioral)5 * --------------------6 * INTENT: encapsulate a request as an object, allowing queuing, logging, and undo.7 * UML: Command + execute()/undo() ; Invoker triggers; Receiver does the work.8 * PROS: decouples invoker from receiver; supports undo/redo and macros.9 * CONS: many command classes.10 * REAL-WORLD: Runnable, GUI actions, transaction logs, undo stacks.11 */12import java.util.*;13 14public class patterns14CommandPattern {15 16    interface Command { void execute(); void undo(); }17 18    // Receiver19    static class Light {20        private boolean on;21        void on()  { on = true;  System.out.println("Light ON"); }22        void off() { on = false; System.out.println("Light OFF"); }23    }24 25    static class LightOnCommand implements Command {26        private final Light light;27        LightOnCommand(Light l) { light = l; }28        public void execute() { light.on(); }29        public void undo() { light.off(); }30    }31 32    // Invoker with undo history33    static class RemoteControl {34        private final Deque<Command> history = new ArrayDeque<>();35        void press(Command c) { c.execute(); history.push(c); }36        void undoLast() {37            if (!history.isEmpty()) { System.out.print("undo -> "); history.pop().undo(); }38        }39    }40 41    public static void main(String[] args) {42        RemoteControl remote = new RemoteControl();43        Command lightOn = new LightOnCommand(new Light());44        remote.press(lightOn);45        remote.press(lightOn);46        remote.undoLast();47        remote.undoLast();48    }49}