added singleton sample

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;
+	}
+}