code: public static String concat(final String a, final String b) {
          final StringBuilder sb = Objectory.createStringBuilder();
  
          try {
              return sb.append(a).append(b).toString();
          } finally {
              Objectory.recycle(sb);
          }
      }
docs: Returns <code>a + b</code>
  
  @param a
  @param b
  @return