Method isPlainString

classpath/java/util/regex/PikeVM.java:471–494

Determines whether this machine recognizes a pattern without special operators. In case that the regular expression is actually a plain string without any special operators, we can avoid using a full-blown Pike VM and instead fall back to using the much faster TrivialPattern. @retu

()

   *         non-trivial pattern
   */
  public String isPlainString() {
    // we expect the machine to start with the find preamble and SAVE_OFFSET 0
    // end with SAVE_OFFSET 1
    int start = findPrefixLength;
    if (start + 1 < program.length &&
        program[start] == SAVE_OFFSET && program[start + 1] == 0) {
      start += 2;
    }
    int end = program.length;
    if (end > start + 1 &&
        program[end - 2] == SAVE_OFFSET && program[end - 1] == 1) {
      end -= 2;
    }
    for (int i = start; i < end; ++ i) {
      if (program[i] < 0) {
        return null;
      }
    }
    char[] array = new char[end - start];
    for (int i = start; i < end; ++ i) {
      array[i - start] = (char)program[i];
    }
    return new String(array);
  }

  private static int length(int opcode) {
    return opcode <= SINGLE_ARG_START && opcode >= SINGLE_ARG_END ? 2 : 1;