added command sample

command/pom.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0"?>
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+  <groupId>com.iluwatar</groupId>
+  <artifactId>command</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <name>command</name>
+  <url>http://maven.apache.org</url>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>3.8.1</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

command/src/main/java/com/iluwatar/App.java

@@ -0,0 +1,20 @@
+package com.iluwatar;
+
+public class App 
+{
+    public static void main( String[] args )
+    {
+    	Wizard wizard = new Wizard();
+    	Goblin goblin = new Goblin();
+
+    	goblin.printStatus();
+    	
+    	wizard.castSpell(new ShrinkSpell(), goblin);
+    	goblin.printStatus();
+    	
+    	wizard.castSpell(new InvisibilitySpell(), goblin);
+    	goblin.printStatus();
+    	wizard.undoLastSpell();
+    	goblin.printStatus();
+    }
+}

command/src/main/java/com/iluwatar/Command.java

@@ -0,0 +1,12 @@
+package com.iluwatar;
+
+public abstract class Command {
+
+	public abstract void execute(Target target);
+	
+	public abstract void undo();
+
+	@Override
+	public abstract String toString();	
+	
+}

command/src/main/java/com/iluwatar/Goblin.java

@@ -0,0 +1,15 @@
+package com.iluwatar;
+
+public class Goblin extends Target {
+
+	public Goblin() {
+		this.setSize(Size.NORMAL);
+		this.setVisibility(Visibility.VISIBLE);
+	}
+	
+	@Override
+	public String toString() {
+		return "Goblin";
+	}
+
+}

command/src/main/java/com/iluwatar/InvisibilitySpell.java

@@ -0,0 +1,28 @@
+package com.iluwatar;
+
+public class InvisibilitySpell extends Command {
+
+	private Target target;
+	
+	public InvisibilitySpell() {
+		target = null;
+	}
+	
+	@Override
+	public void execute(Target target) {
+		target.setVisibility(Visibility.INVISIBLE);
+		this.target = target;
+	}
+
+	@Override
+	public void undo() {
+		if (target != null) {
+			target.setVisibility(Visibility.VISIBLE);
+		}
+	}
+
+	@Override
+	public String toString() {
+		return "Invisibility spell";
+	}
+}

command/src/main/java/com/iluwatar/ShrinkSpell.java

@@ -0,0 +1,32 @@
+package com.iluwatar;
+
+public class ShrinkSpell extends Command {
+
+	private Size oldSize;
+	
+	private Target target;
+	
+	public ShrinkSpell() {
+		oldSize = null;
+		target = null;
+	}
+	
+	@Override
+	public void execute(Target target) {
+		oldSize = target.getSize();
+		target.setSize(Size.SMALL);
+		this.target = target;
+	}
+
+	@Override
+	public void undo() {
+		if (oldSize != null && target != null) {
+			target.setSize(oldSize);
+		}
+	}
+
+	@Override
+	public String toString() {
+		return "Shrink spell";
+	}
+}

command/src/main/java/com/iluwatar/Size.java

@@ -0,0 +1,31 @@
+package com.iluwatar;
+
+public enum Size {
+
+	SMALL,
+	NORMAL,
+	LARGE;
+
+	@Override
+	public String toString() {
+		
+		String s = "";
+		
+		switch (this) {
+		case LARGE:
+			s = "large";
+			break;
+		case NORMAL:
+			s = "normal";
+			break;
+		case SMALL:
+			s = "small";
+			break;
+		default:
+			break;
+		}
+		return s;
+	}
+
+	
+}

command/src/main/java/com/iluwatar/Target.java

@@ -0,0 +1,31 @@
+package com.iluwatar;
+
+public abstract class Target {
+
+	private Size size;
+
+	private Visibility visibility;
+	
+	public Size getSize() {
+		return size;
+	}
+
+	public void setSize(Size size) {
+		this.size = size;
+	}
+
+	public Visibility getVisibility() {
+		return visibility;
+	}
+
+	public void setVisibility(Visibility visibility) {
+		this.visibility = visibility;
+	}
+
+	@Override
+	public abstract String toString();
+	
+	public void printStatus() {
+		System.out.println(String.format("%s, size=%s visibility=%s", this, getSize(), getVisibility()));
+	}
+}

command/src/main/java/com/iluwatar/Visibility.java

@@ -0,0 +1,26 @@
+package com.iluwatar;
+
+public enum Visibility {
+
+	VISIBLE,
+	INVISIBLE;
+
+	@Override
+	public String toString() {
+		
+		String s = "";
+		
+		switch (this) {
+		case INVISIBLE:
+			s = "invisible";
+			break;
+		case VISIBLE:
+			s = "visible";
+			break;
+		default:
+			break;
+		
+		}
+		return s;
+	}
+}

command/src/main/java/com/iluwatar/Wizard.java

@@ -0,0 +1,31 @@
+package com.iluwatar;
+
+public class Wizard extends Target {
+
+	private Command previousSpell;
+	
+	public Wizard() {
+		this.setSize(Size.NORMAL);
+		this.setVisibility(Visibility.VISIBLE);
+		previousSpell = null;
+	}
+	
+	public void castSpell(Command command, Target target) {
+		System.out.println(this + " casts " + command + " at " + target);
+		command.execute(target);
+		previousSpell = command;
+	}
+
+	public void undoLastSpell() {
+		if (previousSpell != null) {
+			System.out.println(this + " undoes " + previousSpell);
+			previousSpell.undo();
+		}
+	}
+	
+	@Override
+	public String toString() {
+		return "Wizard";
+	}
+	
+}

pom.xml

@@ -31,6 +31,7 @@
     <module>flyweight</module>
     <module>proxy</module>
     <module>chain</module>
+    <module>command</module>
   </modules>
   
 <build>