String to long converter

StringLongConverter.java

/**
 * The Class StringLongConverter.
 */
public class StringLongConverter {
  /**
   * This method converts a String to long value.
   * 
   * @param stringToBeConverted the string to be converted
   * @return the long value
   */
  public long stringToLong(String stringToBeConverted) {
    int length = stringToBeConverted.length();
    boolean isNeg = stringToBeConverted.charAt(0) == '-';
    long longValue = 0;
    int startIndex = isNeg ? 1 : 0;
    char zero = '0';
    int zeroAsciiVal = (int) zero;

    while (length > startIndex) {
      longValue *= 10;
      int charVal =
          stringToBeConverted.charAt(startIndex) - zeroAsciiVal;
      if (charVal < 0 | charVal > 9)
        throw new NumberFormatException();
      longValue += charVal;
      startIndex++;
    }
    return isNeg ? -longValue : longValue;
  }

  /**
   * The main method.
   * 
   * @param args the arguments
   */
  public static void main(String[] args) {
    long i = new StringLongConverter().stringToLong("123");
    if (i == 123)
      System.out.println("Success ! " + i);
    else
      System.out.println("Failure");
  }

}