make RandomString utility class

Author: vladak

src/org/opensolaris/opengrok/util/RandomString.java

@@ -23,11 +23,17 @@
 package org.opensolaris.opengrok.util;
 
 /**
+ * Utility class that can generate various random strings.
  *
  * @author Krystof Tulinger
  */
-public class RandomString {
+public final class RandomString {
 
+    private RandomString() {
+        // Throw an exception if this ever *is* called.
+	throw new AssertionError("Instantiating utility class " + getClass());
+    }
+
     public static String generateLower(int length) {
         return generate(length, "abcdefghijklmnopqrstuvwxyz");
     }