Remove old methods in Messages and add StringUtils tests

StringUtils - merge the two join methods to one common implementation with two interface; add tests

Messages - remove the methods taking a String as code after the kind refactoring by @DNx5

src/main/java/fr/xephi/authme/settings/Messages.java

@@ -7,6 +7,7 @@ import org.bukkit.command.CommandSender;
 import java.io.File;
 
 /**
+ * Class for retrieving and sending translatable messages to players.
  */
 // TODO ljacqu 20151124: This class is a weird mix between singleton and POJO
 // TODO: change it into POJO
@@ -15,7 +16,7 @@ public class Messages extends CustomConfiguration {
     /** The section symbol, used in Minecraft for formatting codes. */
     private static final String SECTION_SIGN = "\u00a7";
     private static Messages singleton;
-    private String language = "en";
+    private String language;
 
 
     /**
@@ -51,42 +52,27 @@ public class Messages extends CustomConfiguration {
     }
 
     /**
-     * Send the given message code to the player.
+     * Retrieve the message from the text file and return it split by new line as an array.
      *
-     * @param sender The entity to send the message to
-     * @param msg The message code to send
+     * @param key The message key to retrieve
      *
-     * @deprecated Use {@link Messages#send(CommandSender, MessageKey)} instead
+     * @return The message split by new lines
      */
-    @Deprecated
-    public void send(CommandSender sender, String msg) {
-        String[] lines = retrieve(msg);
-        for (String line : lines) {
-            sender.sendMessage(line);
-        }
-    }
-
     public String[] retrieve(MessageKey key) {
         return retrieve(key.getKey());
     }
 
+    /**
+     * Retrieve the message from the text file.
+     *
+     * @param key The message key to retrieve
+     *
+     * @return The message from the file
+     */
     public String retrieveSingle(MessageKey key) {
         return StringUtils.join("\n", retrieve(key.getKey()));
     }
 
-    /**
-     * Retrieve the message from the text file and returns it split by new line as an array.
-     *
-     * @param msg The message code to retrieve
-     *
-     * @return The message split by new lines
-     * @deprecated Use {@link Messages#retrieve(MessageKey)} instead.
-     */
-    @Deprecated
-    public String[] send(String msg) {
-        return retrieve(msg);
-    }
-
     /**
      * Retrieve the message from the configuration file.
      *

src/main/java/fr/xephi/authme/util/StringUtils.java

@@ -6,6 +6,7 @@ import net.ricecode.similarity.StringSimilarityServiceImpl;
 
 import java.io.PrintWriter;
 import java.io.StringWriter;
+import java.util.Arrays;
 
 /**
  * Utility class for String operations.
@@ -79,6 +80,9 @@ public final class StringUtils {
      * @return a new String that is composed of the elements separated by the delimiter
      */
     public static String join(String delimiter, Iterable<String> elements) {
+        if (delimiter == null) {
+            delimiter = "";
+        }
         StringBuilder sb = new StringBuilder();
         for (String element : elements) {
             if (!isEmpty(element)) {
@@ -101,21 +105,8 @@ public final class StringUtils {
      *
      * @return a new String that is composed of the elements separated by the delimiter
      */
-    public static String join(CharSequence delimiter, CharSequence... elements) {
-        if (elements.length == 0) {
-            return "";
-        }
-        if (delimiter == null) {
-            delimiter = "";
-        }
-        StringBuilder sb = new StringBuilder(elements[0]);
-        if (elements.length > 1) {
-            for (int i = 1; i < elements.length; i++) {
-                sb.append(delimiter);
-                sb.append(elements[i]);
-            }
-        }
-        return sb.toString();
+    public static String join(String delimiter, String... elements) {
+        return join(delimiter, Arrays.asList(elements));
     }
 
     /**