Merge pull request iluwatar#19 from Alwayswithme/master

enum approach of singleton

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

@@ -5,6 +5,8 @@
  * Singleton pattern ensures that the class (IvoryTower) can have only one
  * existing instance and provides global access to that instance.
  *
+ * http://stackoverflow.com/questions/70689/what-is-an-efficient-way-to-implement-a-singleton-pattern-in-java
+ *
  */
 public class App {
 
@@ -22,5 +24,9 @@ public static void main(String[] args) {
 		System.out.println("threadSafeIvoryTower1=" + threadSafeIvoryTower1);
 		System.out.println("threadSafeIvoryTower2=" + threadSafeIvoryTower2);
 
+		EnumIvoryTower enumIvoryTower1 = EnumIvoryTower.INSTANCE;
+		EnumIvoryTower enumIvoryTower2 = EnumIvoryTower.INSTANCE;
+		System.out.println("enumIvoryTower1=" + enumIvoryTower1);
+		System.out.println("enumIvoryTower2=" + enumIvoryTower2);
 	}
 }

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

@@ -0,0 +1,15 @@
+package com.iluwatar;
+
+/**
+ *
+ * Enum Singleton class.
+ *
+ */
+public enum EnumIvoryTower {
+    INSTANCE;
+
+    @Override
+    public String toString() {
+        return getDeclaringClass().getCanonicalName() + "@" + hashCode();
+    }
+}