Merge pull request #20 from darbyluv2code/feature/add-command-pattern

Add Command Pattern

Author: darbyluv2code

section-04-behavioral-design-patterns/16-command/pom.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.luv2code</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.0</version>
+
+    <properties>
+        <maven.compiler.source>25</maven.compiler.source>
+        <maven.compiler.target>25</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+</project>

section-04-behavioral-design-patterns/16-command/src/main/java/com/luv2code/designpatterns/behavioral/command/Light.java

@@ -0,0 +1,39 @@
+package com.luv2code.designpatterns.behavioral.command;
+
+/**
+ * Role: Receiver
+ *
+ * Knows how to perform the actual lighting operations.
+ * Has no knowledge of the Command pattern.
+ */
+public class Light {
+
+    private String location;
+
+    public Light(String location) {
+        this.location = location;
+    }
+
+    public String getLocation() {
+        return location;
+    }
+
+    public void turnOn() {
+        System.out.println("[Device] " + location + " light -> ON");
+    }
+
+    public void turnOff() {
+        System.out.println("[Device] " + location + " light -> OFF");
+    }
+
+}
+
+
+
+
+
+
+
+
+
+

section-04-behavioral-design-patterns/16-command/src/main/java/com/luv2code/designpatterns/behavioral/command/LightOffCommand.java

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+package com.luv2code.designpatterns.behavioral.command;
+
+/**
+ * Role: ConcreteCommand
+ *
+ * Turns a Light off.
+ * Undo turns the light on.
+ */
+public class LightOffCommand implements SmartHomeCommand {
+
+    private Light light;
+
+    public LightOffCommand(Light light) {
+        this.light = light;
+    }
+
+    @Override
+    public void execute() {
+        light.turnOff();
+    }
+
+    @Override
+    public void undo() {
+        light.turnOn();
+    }
+
+    @Override
+    public String getDescription() {
+        return "Turn " + light.getLocation() + " light OFF";
+    }
+}

section-04-behavioral-design-patterns/16-command/src/main/java/com/luv2code/designpatterns/behavioral/command/LightOnCommand.java

@@ -0,0 +1,31 @@
+package com.luv2code.designpatterns.behavioral.command;
+
+/**
+ * Role: ConcreteCommand
+ *
+ * Turns a Light on.
+ * Undo turns the light off.
+ */
+public class LightOnCommand implements SmartHomeCommand {
+
+    private Light light;
+
+    public LightOnCommand(Light light) {
+        this.light = light;
+    }
+
+    @Override
+    public void execute() {
+        light.turnOn();
+    }
+
+    @Override
+    public void undo() {
+        light.turnOff();
+    }
+
+    @Override
+    public String getDescription() {
+        return "Turn " + light.getLocation() + " light ON";
+    }
+}

section-04-behavioral-design-patterns/16-command/src/main/java/com/luv2code/designpatterns/behavioral/command/MainApp.java

@@ -0,0 +1,74 @@
+package com.luv2code.designpatterns.behavioral.command;
+
+/**
+ * Role: Client
+ *
+ * Demonstrates the Command pattern.
+ * The RemoteControl (Invoker) is reused across all demos without modification.
+ */
+public class MainApp {
+
+    static void main() {
+
+        System.out.println("--- Demo 1: Smart Home Demo ---");
+        runSmartHomeDemo();
+
+        System.out.println("\n--- Demo 2: Thermostat Demo ---");
+        runThermostatDemo();
+
+        System.out.println("\n--- Demo 3: Pet Food Demo ---");
+        runPetFoodDemo();
+    }
+
+    private static void runPetFoodDemo() {
+
+        PetFoodDispenser petFoodDispenser = new PetFoodDispenser("Max");
+        RemoteControl remoteControl = new RemoteControl();
+
+        remoteControl.pressButton(new PetFoodDispenserCommand(petFoodDispenser));
+
+        // Attempting undo
+        remoteControl.pressUndo();
+    }
+
+    private static void runThermostatDemo() {
+
+        Thermostat thermostat = new Thermostat(18);
+        RemoteControl remoteControl = new RemoteControl();
+
+        remoteControl.pressButton(new ThermostatSetCommand(thermostat, 22));
+
+        System.out.println("\n-- Undoing temperature change ---");
+        remoteControl.pressUndo();
+    }
+
+    private static void runSmartHomeDemo() {
+
+        Light livingRoomLight = new Light("Living Room");
+        RemoteControl remoteControl = new RemoteControl();
+
+        remoteControl.pressButton(new LightOnCommand(livingRoomLight));
+        remoteControl.pressButton(new LightOffCommand(livingRoomLight));
+
+        System.out.println();
+        remoteControl.printHistory();
+    }
+}
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+

section-04-behavioral-design-patterns/16-command/src/main/java/com/luv2code/designpatterns/behavioral/command/PetFoodDispenser.java

@@ -0,0 +1,20 @@
+package com.luv2code.designpatterns.behavioral.command;
+
+/**
+ * Role: Receiver
+ *
+ * Knows how to dispense a single serving of pet food.
+ * Has no knowledge of the Command pattern.
+ */
+public class PetFoodDispenser {
+
+    private String petName;
+
+    public PetFoodDispenser(String petName) {
+        this.petName = petName;
+    }
+
+    public void dispense() {
+        System.out.println("[Device] Dispensing one serving for " + petName);
+    }
+}

section-04-behavioral-design-patterns/16-command/src/main/java/com/luv2code/designpatterns/behavioral/command/PetFoodDispenserCommand.java

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+package com.luv2code.designpatterns.behavioral.command;
+
+/**
+ * Role: ConcreteCommand
+ *
+ * Dispenses a single serving of pet food.
+ * This action is irreversible - undo does nothing.
+ */
+public class PetFoodDispenserCommand implements SmartHomeCommand {
+
+    private PetFoodDispenser petFoodDispenser;
+
+    public PetFoodDispenserCommand(PetFoodDispenser petFoodDispenser) {
+        this.petFoodDispenser = petFoodDispenser;
+    }
+
+    @Override
+    public void execute() {
+        petFoodDispenser.dispense();
+    }
+
+    @Override
+    public void undo() {
+        System.out.println("[Command] Cannot undo: food already dispensed.");
+    }
+
+    @Override
+    public String getDescription() {
+        return "Dispense pet food serving";
+    }
+}

section-04-behavioral-design-patterns/16-command/src/main/java/com/luv2code/designpatterns/behavioral/command/RemoteControl.java

@@ -0,0 +1,58 @@
+package com.luv2code.designpatterns.behavioral.command;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/**
+ * Role: Invoker
+ *
+ * Triggers commands and maintains a history stack for undo support.
+ * Depends only on the SmartHomeCommand interface.
+ */
+public class RemoteControl {
+
+    private Deque<SmartHomeCommand> history = new ArrayDeque<>();
+
+    public void pressButton(SmartHomeCommand command) {
+        if (command == null) {
+            throw new IllegalArgumentException("Command cannot be null");
+        }
+
+        command.execute();
+        history.push(command);
+    }
+
+    public void pressUndo() {
+        if (history.isEmpty()) {
+            System.out.println("[Remote] Nothing to undo.");
+        }
+
+        SmartHomeCommand command = history.pop();
+        System.out.println("[Remote] Undoing: " + command.getDescription());
+        command.undo();
+    }
+
+    public void printHistory() {
+        System.out.println("[Remote] Command History (most recent first):");
+
+        if (history.isEmpty()) {
+            System.out.println("  (empty)");
+        } else {
+            for (SmartHomeCommand tempCommand : history) {
+                System.out.println(" - " + tempCommand.getDescription());
+            }
+        }
+    }
+
+}
+
+
+
+
+
+
+
+
+
+
+

section-04-behavioral-design-patterns/16-command/src/main/java/com/luv2code/designpatterns/behavioral/command/SmartHomeCommand.java

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+package com.luv2code.designpatterns.behavioral.command;
+
+/**
+ * Role: Command
+ *
+ * Declares the contract for all smart home commands.
+ * Every concrete command must support execute, undo and a description.
+ */
+public interface SmartHomeCommand {
+
+    void execute();
+
+    void undo();
+
+    String getDescription();
+}

section-04-behavioral-design-patterns/16-command/src/main/java/com/luv2code/designpatterns/behavioral/command/Thermostat.java

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+package com.luv2code.designpatterns.behavioral.command;
+
+/**
+ * Role: Receiver
+ *
+ * Knows how to perform temperature changes.
+ * Has no knowledge of the Command pattern.
+ */
+public class Thermostat {
+
+    private int temperatureCelsius;
+
+    public Thermostat(int temperatureCelsius) {
+        this.temperatureCelsius = temperatureCelsius;
+    }
+
+    public int getTemperatureCelsius() {
+        return temperatureCelsius;
+    }
+
+    public void setTemperatureCelsius(int temperatureCelsius) {
+        System.out.println("[Device] Thermostat: " + this.temperatureCelsius
+                + "C -> " + temperatureCelsius + "C");
+        this.temperatureCelsius = temperatureCelsius;
+    }
+}