fix: upgrade checkstyle and fix findings

Author: iluwatar

build.gradle

@@ -18,7 +18,7 @@ configurations {
 // Apply the checkstyle plugin
 apply plugin: 'checkstyle'
 checkstyle {
-    toolVersion = '10.3.4'
+    toolVersion = '10.21.4'
     config = resources.text.fromArchiveEntry(configurations.checkstyleConfig, 'google_checks.xml')
     maxErrors = 0
     maxWarnings = 0

src/main/java/algorithm/LuhnModnSnippet.java

@@ -59,6 +59,11 @@ public static char characterFromCodePoint(int codePoint) {
     return CODE_POINTS.charAt(codePoint);
   }
 
+  /**
+   * Returns the number of valid input characters.
+   *
+   * @return num valid input characters
+   */
   public static int numberOfValidInputCharacters() {
     return CODE_POINTS.length();
   }

src/main/java/array/ArrayConcatSnippet.java

@@ -32,7 +32,7 @@
 public class ArrayConcatSnippet {
 
   /**
-   * Generic 2 array concatenation Credits: Joachim Sauer https://stackoverflow.com/questions/80476/how-can-i-concatenate-two-arrays-in-java
+   * Generic 2 array concatenation Credits: Joachim Sauer https://stackoverflow.com/questions/80476/how-can-i-concatenate-two-arrays-in-java.
    *
    * @param first  is the first array (not null)
    * @param second is the second array (not null)

src/main/java/array/MultiArrayConcatenationSnippet.java

@@ -32,7 +32,7 @@
 public class MultiArrayConcatenationSnippet {
 
   /**
-   * Generic N array concatenation Credits: Joachim Sauer https://stackoverflow.com/questions/80476/how-can-i-concatenate-two-arrays-in-java
+   * Generic N array concatenation Credits: Joachim Sauer https://stackoverflow.com/questions/80476/how-can-i-concatenate-two-arrays-in-java.
    *
    * @param first is the first array (not null)
    * @param rest  the rest of the arrays (optional)

src/main/java/cls/CreatingObjectSnippet.java

@@ -37,14 +37,14 @@ public class CreatingObjectSnippet {
    * @param cls fully qualified name of class includes the package name as String
    * @return object
    * @throws NoSuchMethodException if a method that does not exist at runtime.
-   * @throws IllegalAccessException <p>if an currently executing method does not have access to
-   *     the definition of the specified class, field, method or constructor</p>
-   * @throws InvocationTargetException <p>InvocationTargetException is a checked exception
-   *     that wraps an exception thrown by an invoked method or constructor.</p>
-   * @throws InstantiationException <p>when an method tries to create an instance of a class
-   *     using the newInstance method in class Class.</p>
-   * @throws ClassNotFoundException <p>when an application tries to load in a class
-   *     through its string name.</p>
+   * @throws IllegalAccessException if an currently executing method does not have access to
+   *     the definition of the specified class, field, method or constructor
+   * @throws InvocationTargetException InvocationTargetException is a checked exception
+   *     that wraps an exception thrown by an invoked method or constructor.
+   * @throws InstantiationException when an method tries to create an instance of a class
+   *     using the newInstance method in class Class.
+   * @throws ClassNotFoundException when an application tries to load in a class
+   *     through its string name.
    */
   public static Object createObject(String cls)
           throws NoSuchMethodException,

src/main/java/thread/ThreadPool.java

@@ -33,8 +33,8 @@
 public class ThreadPool {
 
   /**
-   * <p>Creates pool of threads. Where the pool is the size of the number of processors
-   * available to the Java virtual machine.</p>
+   * Creates pool of threads. Where the pool is the size of the number of processors
+   * available to the Java virtual machine.
    *
    * @return the newly created thread pool
    */