title: Java Library Commons Lang3 'ClassNotFoundException' error
body: <pre><code>import java.util.Arrays;
  import org.apache.commons.lang3.ArrayUtils;
  
  public class MonsterGame {
  
      public static void main(String[] args)
      {
  
          Monster.buildBattleBoard();
  
          char[][] tempBattleBoard = new char[10][10];
  
          // ObjectName[] ArrayName = new ObjectName[4];
  
          Monster[] Monsters = new Monster[4];
  
          // Monster(int health, int attack, int movement, String name)
  
          Monsters[0] = new Monster(1000, 20, 1, "Frank");
          Monsters[1] = new Monster(500, 40, 2, "Drac");
          Monsters[2] = new Monster(1000, 20, 1, "Paul");
          Monsters[3] = new Monster(1000, 20, 1, "George");
  
          Monster.redrawBoard();
  
  
      for (Monster m : Monsters) {
          if(m.getAlive()) {
              int arrayItemIndex = ArrayUtils.indexOf(Monsters, m);
              m.moveMonster(Monsters, arrayItemIndex);
          }
      }
  
      Monster.redrawBoard();
  
  
  }
  }
  </code></pre>
  
  <p>When trying to run this code, I get this error:</p>
  
  <pre><code>Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/lang3/ArrayUtils
      at MonsterGame.main(MonsterGame.java:55)
  Caused by: java.lang.ClassNotFoundException: org.apache.commons.lang3.ArrayUtils
      at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:602)
      at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
      at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
      ... 1 more
  </code></pre>
  
  <p>I have two files, in the same package. I've only shown this one because I do not believe the other file is the problem.
  I followed a tutorial on how to use java libraries: download, import, build path etc.</p>
  
  <p>The problem here is, the import seems to be fine but actually using the library is the problem.</p>
  
  <p>I'm very new to Java so sorry if this is a very simple error to fix.</p>
  
  <p>Thank you for any response/feedback in advance.</p>