added singleton sample

pom.xml

@@ -22,5 +22,6 @@
     <module>builder</module>
     <module>factory-method</module>
     <module>prototype</module>
+    <module>singleton</module>
   </modules>
 </project>

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

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

@@ -0,0 +1,14 @@
+package com.iluwatar;
+
+public class App 
+{
+    public static void main( String[] args )
+    {
+    	
+    	IvoryTower ivoryTower1 = IvoryTower.getInstance();
+    	IvoryTower ivoryTower2 = IvoryTower.getInstance();
+    	System.out.println("ivoryTower1=" + ivoryTower1);
+    	System.out.println("ivoryTower2=" + ivoryTower2);
+    	
+    }
+}

singleton/src/main/java/com/iluwatar/IvoryTower.java

@@ -0,0 +1,13 @@
+package com.iluwatar;
+
+public class IvoryTower {
+
+	private static IvoryTower instance = new IvoryTower();
+	
+	private IvoryTower() {
+	}
+
+	public static IvoryTower getInstance() {
+		return instance;
+	}
+}