public int nextToken() {
    // Skip any leading white space
    while (index < length && Character.isWhitespace(expr[index])) {
      index++;
    }
    // Clear the current token val
    tokenVal = null;
    if (index == length) return TOKEN_END; // End of string
    int start = index;
    char currentChar = expr[index];
    char nextChar = (char)0;
    index++;
    if (index < length) nextChar = expr[index];
    // Check for a known token start
    switch (currentChar) {
      case '(' -> {
        return TOKEN_LBRACE;
      }
      case ')' -> {
        return TOKEN_RBRACE;
      }
      case '=' -> {
        return TOKEN_EQ;
      }
      case '!' -> {
        if (nextChar == '=') {
          index++;
          return TOKEN_NOT_EQ;
        }
        return TOKEN_NOT;
      }
      case '|' -> {
        if (nextChar == '|') {
          index++;
          return TOKEN_OR;
        }
      }
      case '&' -> {
        if (nextChar == '&') {
          index++;
          return TOKEN_AND;
        }
      }
      case '>' -> {
        if (nextChar == '=') {
          index++;
          return TOKEN_GE; // Greater than or equal
        }
        return TOKEN_GT; // Greater than
      }
      case '<' -> {
        if (nextChar == '=') {
          index++;
          return TOKEN_LE; // Less than or equal
        }
        return TOKEN_LT; // Less than
      }
      default -> { }
      // Otherwise it's a string
    }
    int end = index;
    if (currentChar == '"' || currentChar == '\'') {
      // It's a quoted string and the end is the next unescaped quote
      char endChar = currentChar;
      boolean escaped = false;
      start++;
      for (; index < length; index++) {
        if (expr[index] == '\\' && !escaped) {
          escaped = true;
          continue;
        }
        if (expr[index] == endChar && !escaped) break;
        escaped = false;
      }
      end = index;
      index++; // Skip the end quote
    }
    else if (currentChar == '/') {
      // It's a regular expression and the end is the next unescaped /
      char endChar = currentChar;
      boolean escaped = false;
      for (; index < length; index++) {
        if (expr[index] == '\\' && !escaped) {
          escaped = true;
          continue;
        }
        if (expr[index] == endChar && !escaped) break;
        escaped = false;
      }
      end = ++index;
    }
    else {
      // End is the next whitespace character
      for (; index < length; index++) {
        if (isMetaChar(expr[index])) break;
      }
      end = index;
    }
    // Extract the string from the array
    this.tokenVal = new String(expr, start, end - start);
    return TOKEN_STRING;
  }
public int nextToken()