#107 JavaDoc for Singleton

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

@@ -1,51 +1,55 @@
-package com.iluwatar.singleton;
-
-/**
- *
- * Singleton pattern ensures that the class (IvoryTower) can have only one
- * existing instance per java classloader instance and provides global access to it. 
- * 
- * http://stackoverflow.com/questions/70689/what-is-an-efficient-way-to-implement-a-singleton-pattern-in-java
- *
- * The risk of this pattern is that bugs resulting from setting a singleton up in a distributed environment can 
- * be tricky to debug, since it will work fine if you debug with a single classloader. Additionally, these
- * problems can crop up a while after the implementation of a singleton, since they may start out synchronous and
- * only become async with time, so you it may not be clear why you are seeing certain changes in behaviour.
- * 
- * http://stackoverflow.com/questions/17721263/singleton-across-jvm-or-application-instance-or-tomcat-instance
- */
-public class App {
-
-	public static void main(String[] args) {
-
-		// eagerly initialized singleton
-		IvoryTower ivoryTower1 = IvoryTower.getInstance();
-		IvoryTower ivoryTower2 = IvoryTower.getInstance();
-		System.out.println("ivoryTower1=" + ivoryTower1);
-		System.out.println("ivoryTower2=" + ivoryTower2);
-
-		// lazily initialized singleton
-		ThreadSafeLazyLoadedIvoryTower threadSafeIvoryTower1 = ThreadSafeLazyLoadedIvoryTower
-				.getInstance();
-		ThreadSafeLazyLoadedIvoryTower threadSafeIvoryTower2 = ThreadSafeLazyLoadedIvoryTower
-				.getInstance();
-		System.out.println("threadSafeIvoryTower1=" + threadSafeIvoryTower1);
-		System.out.println("threadSafeIvoryTower2=" + threadSafeIvoryTower2);
-
-		// enum singleton
-		EnumIvoryTower enumIvoryTower1 = EnumIvoryTower.INSTANCE;
-		EnumIvoryTower enumIvoryTower2 = EnumIvoryTower.INSTANCE;
-		System.out.println("enumIvoryTower1=" + enumIvoryTower1);
-		System.out.println("enumIvoryTower2=" + enumIvoryTower2);
-		
-		InitializingOnDemandHolderIdiom demandHolderIdiom = InitializingOnDemandHolderIdiom.getInstance();
-		System.out.println(demandHolderIdiom);
-		InitializingOnDemandHolderIdiom demandHolderIdiom2 = InitializingOnDemandHolderIdiom.getInstance();
-		System.out.println(demandHolderIdiom2);
-		
-		ThreadSafeDoubleCheckLocking dcl1 = ThreadSafeDoubleCheckLocking.getInstance();
-		System.out.println(dcl1);
-		ThreadSafeDoubleCheckLocking dcl2 = ThreadSafeDoubleCheckLocking.getInstance();
-		System.out.println(dcl2);
-	}
-}
+package com.iluwatar.singleton;
+
+/**
+ *
+ * Singleton pattern ensures that the class ({@link IvoryTower}) can have only one
+ * existing instance per Java classloader instance and provides global access to it. 
+ * <p>
+ * http://stackoverflow.com/questions/70689/what-is-an-efficient-way-to-implement-a-singleton-pattern-in-java
+ *<p>
+ * The risk of this pattern is that bugs resulting from setting a singleton up in a distributed environment can 
+ * be tricky to debug, since it will work fine if you debug with a single classloader. Additionally, these
+ * problems can crop up a while after the implementation of a singleton, since they may start out synchronous and
+ * only become async with time, so you it may not be clear why you are seeing certain changes in behaviour.
+ * <p>
+ * http://stackoverflow.com/questions/17721263/singleton-across-jvm-or-application-instance-or-tomcat-instance
+ */
+public class App {
+
+	/**
+	 * Program entry point
+	 * @param args command line args
+	 */
+	public static void main(String[] args) {
+
+		// eagerly initialized singleton
+		IvoryTower ivoryTower1 = IvoryTower.getInstance();
+		IvoryTower ivoryTower2 = IvoryTower.getInstance();
+		System.out.println("ivoryTower1=" + ivoryTower1);
+		System.out.println("ivoryTower2=" + ivoryTower2);
+
+		// lazily initialized singleton
+		ThreadSafeLazyLoadedIvoryTower threadSafeIvoryTower1 = ThreadSafeLazyLoadedIvoryTower
+				.getInstance();
+		ThreadSafeLazyLoadedIvoryTower threadSafeIvoryTower2 = ThreadSafeLazyLoadedIvoryTower
+				.getInstance();
+		System.out.println("threadSafeIvoryTower1=" + threadSafeIvoryTower1);
+		System.out.println("threadSafeIvoryTower2=" + threadSafeIvoryTower2);
+
+		// enum singleton
+		EnumIvoryTower enumIvoryTower1 = EnumIvoryTower.INSTANCE;
+		EnumIvoryTower enumIvoryTower2 = EnumIvoryTower.INSTANCE;
+		System.out.println("enumIvoryTower1=" + enumIvoryTower1);
+		System.out.println("enumIvoryTower2=" + enumIvoryTower2);
+		
+		InitializingOnDemandHolderIdiom demandHolderIdiom = InitializingOnDemandHolderIdiom.getInstance();
+		System.out.println(demandHolderIdiom);
+		InitializingOnDemandHolderIdiom demandHolderIdiom2 = InitializingOnDemandHolderIdiom.getInstance();
+		System.out.println(demandHolderIdiom2);
+		
+		ThreadSafeDoubleCheckLocking dcl1 = ThreadSafeDoubleCheckLocking.getInstance();
+		System.out.println(dcl1);
+		ThreadSafeDoubleCheckLocking dcl2 = ThreadSafeDoubleCheckLocking.getInstance();
+		System.out.println(dcl2);
+	}
+}

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

@@ -4,12 +4,12 @@ import java.io.Serializable;
 
 /**
  * The Initialize-on-demand-holder idiom is a secure way of 
- * creating lazy initialize singleton Object in Java.
+ * creating lazy initialized singleton object in Java.
  * refer to "The CERT Oracle Secure Coding Standard for Java"
  * By Dhruv Mohindra, Robert C. Seacord p.378
- * 
+ * <p>
  * Singleton objects usually are heavy to create and sometimes need to serialize them.
- * This class also shows how to preserve singleton in Serialized version of singleton.
+ * This class also shows how to preserve singleton in serialized version of singleton.
  * 
  * @author mortezaadi@gmail.com
  *

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

@@ -2,10 +2,11 @@ package com.iluwatar.singleton;
 
 /**
  * Double check locking
- * 
+ * <p>
  * http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
- * 
+ * <p>
  * Broken under Java 1.4.
+ * 
  * @author mortezaadi@gmail.com
  *
  */