added visitor pattern sample

pom.xml

@@ -40,6 +40,7 @@
     <module>state</module>
     <module>strategy</module>
     <module>template-method</module>
+    <module>visitor</module>
   </modules>
   
 <build>

visitor/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>visitor</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <name>visitor</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>

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

@@ -0,0 +1,16 @@
+package com.iluwatar;
+
+public class App 
+{
+    public static void main( String[] args )
+    {
+
+    	Commander commander = new Commander(
+    			new Sergeant(new Soldier(), new Soldier(), new Soldier()), 
+    			new Sergeant(new Soldier(), new Soldier(), new Soldier()));
+    	commander.accept(new SoldierVisitor());
+    	commander.accept(new SergeantVisitor());
+    	commander.accept(new CommanderVisitor());
+    	
+    }
+}

visitor/src/main/java/com/iluwatar/Commander.java

@@ -0,0 +1,19 @@
+package com.iluwatar;
+
+public class Commander extends Unit {
+
+	public Commander(Unit ... children) {
+		super(children);
+	}
+
+	@Override
+	public void accept(UnitVisitor visitor) {
+		visitor.visitCommander(this);
+		super.accept(visitor);
+	}
+	
+	@Override
+	public String toString() {
+		return "commander";
+	}
+}

visitor/src/main/java/com/iluwatar/CommanderVisitor.java

@@ -0,0 +1,22 @@
+package com.iluwatar;
+
+public class CommanderVisitor implements UnitVisitor {
+
+	@Override
+	public void visitSoldier(Soldier soldier) {
+		// TODO Auto-generated method stub
+
+	}
+
+	@Override
+	public void visitSergeant(Sergeant sergeant) {
+		// TODO Auto-generated method stub
+
+	}
+
+	@Override
+	public void visitCommander(Commander commander) {
+		System.out.println("Good to see you " + commander);
+	}
+
+}

visitor/src/main/java/com/iluwatar/Sergeant.java

@@ -0,0 +1,19 @@
+package com.iluwatar;
+
+public class Sergeant extends Unit {
+
+	public Sergeant(Unit ... children) {
+		super(children);
+	}
+
+	@Override
+	public void accept(UnitVisitor visitor) {
+		visitor.visitSergeant(this);
+		super.accept(visitor);
+	}
+	
+	@Override
+	public String toString() {
+		return "sergeant";
+	}
+}

visitor/src/main/java/com/iluwatar/SergeantVisitor.java

@@ -0,0 +1,22 @@
+package com.iluwatar;
+
+public class SergeantVisitor implements UnitVisitor {
+
+	@Override
+	public void visitSoldier(Soldier soldier) {
+		// TODO Auto-generated method stub
+
+	}
+
+	@Override
+	public void visitSergeant(Sergeant sergeant) {
+		System.out.println("Hello " + sergeant);
+	}
+
+	@Override
+	public void visitCommander(Commander commander) {
+		// TODO Auto-generated method stub
+
+	}
+
+}

visitor/src/main/java/com/iluwatar/Soldier.java

@@ -0,0 +1,19 @@
+package com.iluwatar;
+
+public class Soldier extends Unit {
+
+	public Soldier(Unit ... children) {
+		super(children);
+	}
+
+	@Override
+	public void accept(UnitVisitor visitor) {
+		visitor.visitSoldier(this);
+		super.accept(visitor);
+	}
+	
+	@Override
+	public String toString() {
+		return "soldier";
+	}
+}

visitor/src/main/java/com/iluwatar/SoldierVisitor.java

@@ -0,0 +1,22 @@
+package com.iluwatar;
+
+public class SoldierVisitor implements UnitVisitor {
+
+	@Override
+	public void visitSoldier(Soldier soldier) {
+		System.out.println("Greetings " + soldier);
+	}
+
+	@Override
+	public void visitSergeant(Sergeant sergeant) {
+		// TODO Auto-generated method stub
+
+	}
+
+	@Override
+	public void visitCommander(Commander commander) {
+		// TODO Auto-generated method stub
+
+	}
+
+}

visitor/src/main/java/com/iluwatar/Unit.java

@@ -0,0 +1,16 @@
+package com.iluwatar;
+
+public abstract class Unit {
+
+	private Unit[] children;
+
+	public Unit(Unit ... children) {
+		this.children = children;
+	}
+	
+	public void accept(UnitVisitor visitor) {
+		for (Unit child: children) {
+			child.accept(visitor);
+		}
+	}
+}

visitor/src/main/java/com/iluwatar/UnitVisitor.java

@@ -0,0 +1,9 @@
+package com.iluwatar;
+
+public interface UnitVisitor {
+
+	void visitSoldier(Soldier soldier);
+	void visitSergeant(Sergeant sergeant);
+	void visitCommander(Commander commander);
+	
+}