code: public static String concat(String[] values, String delimiter) {
  
      Assert.notNull(values, "The array of String values to concatenate cannot be null!");
  
      StringBuilder buffer = new StringBuilder();
  
      for (String value : values) {
        buffer.append(buffer.length() > 0 ? delimiter : EMPTY_STRING);
        buffer.append(value);
      }
  
      return buffer.toString();
    }
docs: Concatenates the array of Strings into a single String value delimited by the specified delimiter.
  
  @param values an array of Strings to concatenate.
  @param delimiter the String used as the delimiter separating the String values from the array.
  @return a single String value containing all Strings from the array concatenated by the specified delimiter.
  @throws NullPointerException if the String array is null.
  @see java.lang.StringBuilder