diff --git a/singleton/src/main/java/com/iluwatar/singleton/App.java b/singleton/src/main/java/com/iluwatar/singleton/App.java
index 67cb6fd00..11cb4daa6 100644
--- a/singleton/src/main/java/com/iluwatar/singleton/App.java
+++ b/singleton/src/main/java/com/iluwatar/singleton/App.java
@@ -1,55 +1,63 @@
+/**
+ * Singleton pattern.
+ */
+
 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>
+ * 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>
+ * <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) {
+  /**
+   * 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);
+    // 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);
+    // 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);
-	}
+    // 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);
+  }
 }
diff --git a/singleton/src/main/java/com/iluwatar/singleton/EnumIvoryTower.java b/singleton/src/main/java/com/iluwatar/singleton/EnumIvoryTower.java
index 8f9895924..f39babe45 100644
--- a/singleton/src/main/java/com/iluwatar/singleton/EnumIvoryTower.java
+++ b/singleton/src/main/java/com/iluwatar/singleton/EnumIvoryTower.java
@@ -1,17 +1,15 @@
 package com.iluwatar.singleton;
 
 /**
- *
- * Enum Singleton class.
+ * Enum based singleton implementation.
  * Effective Java 2nd Edition (Joshua Bloch) p. 18
- *
  */
 public enum EnumIvoryTower {
-	
-    INSTANCE;
 
-    @Override
-    public String toString() {
-        return getDeclaringClass().getCanonicalName() + "@" + hashCode();
-    }
+  INSTANCE;
+
+  @Override
+  public String toString() {
+    return getDeclaringClass().getCanonicalName() + "@" + hashCode();
+  }
 }
diff --git a/singleton/src/main/java/com/iluwatar/singleton/InitializingOnDemandHolderIdiom.java b/singleton/src/main/java/com/iluwatar/singleton/InitializingOnDemandHolderIdiom.java
index 4fd4c8163..88738b8ca 100644
--- a/singleton/src/main/java/com/iluwatar/singleton/InitializingOnDemandHolderIdiom.java
+++ b/singleton/src/main/java/com/iluwatar/singleton/InitializingOnDemandHolderIdiom.java
@@ -3,34 +3,34 @@ package com.iluwatar.singleton;
 import java.io.Serializable;
 
 /**
- * The Initialize-on-demand-holder idiom is a secure way of 
+ * The Initialize-on-demand-holder idiom is a secure way of
  * 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>
+ * <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.
- * 
- * @author mortezaadi@gmail.com
  *
+ * @author mortezaadi@gmail.com
  */
-public class InitializingOnDemandHolderIdiom implements Serializable{
+public class InitializingOnDemandHolderIdiom implements Serializable {
 
-	private static final long serialVersionUID = 1L;
+  private static final long serialVersionUID = 1L;
 
-	private static class HelperHolder {
-		public static final InitializingOnDemandHolderIdiom INSTANCE = new InitializingOnDemandHolderIdiom();
-	}
+  private InitializingOnDemandHolderIdiom() {
+  }
 
-	public static InitializingOnDemandHolderIdiom getInstance() {
-		return HelperHolder.INSTANCE;
-	}
+  public static InitializingOnDemandHolderIdiom getInstance() {
+    return HelperHolder.INSTANCE;
+  }
 
-	private InitializingOnDemandHolderIdiom() {
-	}
+  protected Object readResolve() {
+    return getInstance();
+  }
 
-	protected Object readResolve() {
-		return getInstance();
-	}
+  private static class HelperHolder {
+    public static final InitializingOnDemandHolderIdiom INSTANCE =
+            new InitializingOnDemandHolderIdiom();
+  }
 
 }
diff --git a/singleton/src/main/java/com/iluwatar/singleton/IvoryTower.java b/singleton/src/main/java/com/iluwatar/singleton/IvoryTower.java
index 5d418aa54..96809c477 100644
--- a/singleton/src/main/java/com/iluwatar/singleton/IvoryTower.java
+++ b/singleton/src/main/java/com/iluwatar/singleton/IvoryTower.java
@@ -1,20 +1,30 @@
 package com.iluwatar.singleton;
 
 /**
- * 
  * Singleton class.
  * Eagerly initialized static instance guarantees thread
  * safety.
- * 
  */
-public class IvoryTower {
+public final class IvoryTower {
 
-	private static IvoryTower instance = new IvoryTower();
+  /**
+   * Static to class instance of the class.
+   */
+  private static IvoryTower instance = new IvoryTower();
 
-	private IvoryTower() {
-	}
+  /**
+   * Private constructor so nobody can instantiate the class.
+   */
+  private IvoryTower() {
+  }
 
-	public static IvoryTower getInstance() {
-		return instance;
-	}
+  /**
+   * To be called by user to
+   * obtain instance of the class.
+   *
+   * @return instance of the singleton.
+   */
+  public static IvoryTower getInstance() {
+    return instance;
+  }
 }
diff --git a/singleton/src/main/java/com/iluwatar/singleton/ThreadSafeDoubleCheckLocking.java b/singleton/src/main/java/com/iluwatar/singleton/ThreadSafeDoubleCheckLocking.java
index d15509236..26b57d4cf 100644
--- a/singleton/src/main/java/com/iluwatar/singleton/ThreadSafeDoubleCheckLocking.java
+++ b/singleton/src/main/java/com/iluwatar/singleton/ThreadSafeDoubleCheckLocking.java
@@ -2,40 +2,44 @@ package com.iluwatar.singleton;
 
 /**
  * Double check locking
- * <p>
+ * <p/>
  * http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
- * <p>
+ * <p/>
  * Broken under Java 1.4.
- * 
- * @author mortezaadi@gmail.com
  *
+ * @author mortezaadi@gmail.com
  */
 public class ThreadSafeDoubleCheckLocking {
-	
-	private static volatile ThreadSafeDoubleCheckLocking INSTANCE;
 
-	/**
-	 * private constructor to prevent client from instantiating.
-	 * 
-	 */
-	private ThreadSafeDoubleCheckLocking() {
-		//to prevent instantiating by Reflection call 
-		if(INSTANCE != null)
-			throw new IllegalStateException("Already initialized.");
-	}
-	
-	public static ThreadSafeDoubleCheckLocking getInstance() {
-		//local variable increases performance by 25 percent 
-		//Joshua Bloch "Effective Java, Second Edition", p. 283-284
-		ThreadSafeDoubleCheckLocking result = INSTANCE;
-		if (result == null) {
-			synchronized (ThreadSafeDoubleCheckLocking.class) {
-				result = INSTANCE;
-				if (result == null) {
-					INSTANCE = result = new ThreadSafeDoubleCheckLocking();
-				}
-			}
-		}
-		return result;
-	}
+  private static volatile ThreadSafeDoubleCheckLocking INSTANCE;
+
+  /**
+   * private constructor to prevent client from instantiating.
+   */
+  private ThreadSafeDoubleCheckLocking() {
+    //to prevent instantiating by Reflection call
+    if (INSTANCE != null) {
+      throw new IllegalStateException("Already initialized.");
+    }
+  }
+
+  /**
+   * Public accessor.
+   *
+   * @return an instance of the class.
+   */
+  public static ThreadSafeDoubleCheckLocking getInstance() {
+    //local variable increases performance by 25 percent
+    //Joshua Bloch "Effective Java, Second Edition", p. 283-284
+    ThreadSafeDoubleCheckLocking result = INSTANCE;
+    if (result == null) {
+      synchronized (ThreadSafeDoubleCheckLocking.class) {
+        result = INSTANCE;
+        if (result == null) {
+          INSTANCE = result = new ThreadSafeDoubleCheckLocking();
+        }
+      }
+    }
+    return result;
+  }
 }
diff --git a/singleton/src/main/java/com/iluwatar/singleton/ThreadSafeLazyLoadedIvoryTower.java b/singleton/src/main/java/com/iluwatar/singleton/ThreadSafeLazyLoadedIvoryTower.java
index f7184cfb0..f9b62e798 100644
--- a/singleton/src/main/java/com/iluwatar/singleton/ThreadSafeLazyLoadedIvoryTower.java
+++ b/singleton/src/main/java/com/iluwatar/singleton/ThreadSafeLazyLoadedIvoryTower.java
@@ -1,28 +1,27 @@
 package com.iluwatar.singleton;
 
 /**
- *
  * Thread-safe Singleton class.
  * The instance is lazily initialized and thus needs synchronization
  * mechanism.
- *
  */
 public class ThreadSafeLazyLoadedIvoryTower {
 
-	private static ThreadSafeLazyLoadedIvoryTower instance = null;
-	
-	private 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();
-		}
+  private ThreadSafeLazyLoadedIvoryTower() {
+  }
 
-		return instance;
-	}
+  /**
+   * The instance gets created only when it is called for first time.
+   * Lazy-loading
+   */
+  public synchronized static ThreadSafeLazyLoadedIvoryTower getInstance() {
+
+    if (instance == null) {
+      instance = new ThreadSafeLazyLoadedIvoryTower();
+    }
+
+    return instance;
+  }
 }