Adjust checkstyle rules. Make checkstyle fail the build when violations are found. Correct all current checkstyle violations.

lazy-loading/src/main/java/com/iluwatar/lazy/loading/Heavy.java

@@ -7,6 +7,9 @@ package com.iluwatar.lazy.loading;
  */
 public class Heavy {
 
+  /**
+   * Constructor
+   */
   public Heavy() {
     System.out.println("Creating Heavy ...");
     try {

lazy-loading/src/main/java/com/iluwatar/lazy/loading/HolderNaive.java

@@ -9,10 +9,16 @@ public class HolderNaive {
 
   private Heavy heavy;
 
+  /**
+   * Constructor
+   */
   public HolderNaive() {
     System.out.println("HolderNaive created");
   }
 
+  /**
+   * Get heavy object
+   */
   public Heavy getHeavy() {
     if (heavy == null) {
       heavy = new Heavy();

lazy-loading/src/main/java/com/iluwatar/lazy/loading/HolderThreadSafe.java

@@ -10,10 +10,16 @@ public class HolderThreadSafe {
 
   private Heavy heavy;
 
+  /**
+   * Constructor
+   */
   public HolderThreadSafe() {
     System.out.println("HolderThreadSafe created");
   }
 
+  /**
+   * Get heavy object
+   */
   public synchronized Heavy getHeavy() {
     if (heavy == null) {
       heavy = new Heavy();

lazy-loading/src/main/java/com/iluwatar/lazy/loading/Java8Holder.java

@@ -5,7 +5,7 @@ import java.util.function.Supplier;
 /**
  * 
  * This lazy loader is thread safe and more efficient than {@link HolderThreadSafe}. It utilizes
- * Java 8 functional interface {@link Supplier<T>} as {@link Heavy} factory.
+ * Java 8 functional interface {@link Supplier} as {@link Heavy} factory.
  *
  */
 public class Java8Holder {