Merge pull request #8 from annemsujan/master

Thread safe lazy loaded singleton implementation added.

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

@@ -1,10 +1,10 @@
 package com.iluwatar;
 
 /**
- * 
+ *
  * Singleton pattern ensures that the class (IvoryTower) can have only one
  * existing instance and provides global access to that instance.
- * 
+ *
  */
 public class App {
 
@@ -15,5 +15,12 @@ public class App {
 		System.out.println("ivoryTower1=" + ivoryTower1);
 		System.out.println("ivoryTower2=" + ivoryTower2);
 
+		ThreadSafeLazyLoadedIvoryTower threadSafeIvoryTower1 = ThreadSafeLazyLoadedIvoryTower
+				.getInstance();
+		ThreadSafeLazyLoadedIvoryTower threadSafeIvoryTower2 = ThreadSafeLazyLoadedIvoryTower
+				.getInstance();
+		System.out.println("threadSafeIvoryTower1=" + threadSafeIvoryTower1);
+		System.out.println("threadSafeIvoryTower2=" + threadSafeIvoryTower2);
+
 	}
 }

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

@@ -0,0 +1,23 @@
+package com.iluwatar;
+
+/**
+ *
+ * Thread-safe Singleton class.
+ *
+ */
+public class ThreadSafeLazyLoadedIvoryTower {
+
+	private static ThreadSafeLazyLoadedIvoryTower instance = null;
+
+	public synchronized static ThreadSafeLazyLoadedIvoryTower getInstance() {
+		/*
+		 * The instance gets created only when it is called for first time.
+		 * Lazy-loading
+		 */
+		if (instance == null) {
+			instance = new ThreadSafeLazyLoadedIvoryTower();
+		}
+
+		return instance;
+	}
+}