Fixed utility classes having constructors.

src/main/java/com/sk89q/util/ArrayUtil.java

@@ -18,7 +18,10 @@
 
 package com.sk89q.util;
 
-public class ArrayUtil {
+public final class ArrayUtil {
+
+    private ArrayUtil() {
+    }
 
     public static String[] removePortionOfArray(String[] array, int from, int to, String replace) {
         String[] newArray = new String[from + array.length - to - (replace == null ? 1 : 0)];

src/main/java/com/sk89q/util/ReflectionUtil.java

@@ -24,7 +24,11 @@ import java.lang.reflect.Field;
 /**
  * @author zml2008
  */
-public class ReflectionUtil {
+public final class ReflectionUtil {
+
+    private ReflectionUtil() {
+    }
+
     @SuppressWarnings("unchecked")
     public static <T> T getField(Object from, String name) {
         Class<?> checkClass = from.getClass();
@@ -39,4 +43,5 @@ public class ReflectionUtil {
         } while (checkClass.getSuperclass() != Object.class && ((checkClass = checkClass.getSuperclass()) != null));
         return null;
     }
+
 }

src/main/java/com/sk89q/util/StringUtil.java

@@ -26,7 +26,11 @@ import java.util.Map;
  * 
  * @author sk89q
  */
-public class StringUtil {
+public final class StringUtil {
+
+    private StringUtil() {
+    }
+
     /**
      * Trim a string if it is longer than a certain length.
      *