Character Validation Performance

Question

I need to validate some strings that I'll be writing to files. I need to validate that the strings only contain the following characters:
{'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p',
'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F',
'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
'W', 'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.',
'-', '(', ')', '/', '=', ',', ' '}The only way I can think to do this is to convert each string into a char[], and then loop through the array to see if each character is valid, but I'm worried that this is going to give really bad performance. What's the fastest way to validate the strings?
p.s I can't use 1.4 so the regex package isn't an option and I can't validate the Strings on input either (they're from an external source).

Answer 1

After writing a test class I found that I was probably over concerned about the performance hit:
public class Tester {
  private static final char[] valid = new char[] {'a', 'b', 'c', 'd', 'e',
       'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
       'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I',
       'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
       'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ' ', '.', '-',
       '(', ')', '/', '=', ','};
  private static final String invalidString =
       "a!a?s$f%f^r&g*t(erfe)_ee+}ee{er~yu@:?k>kik<uluil|oo#454'.;jy5[";
  public Tester() {     
    final long start = System.currentTimeMillis();
    for (int x = 0; x < 100000; x++) validate(invalidString);
    System.out.println(System.currentTimeMillis() - start);     
  public static void main(String[] args) {
    new Tester();
  private String validate(String s) {
    char[] validate = s.toCharArray();
    for (int x = 0; x < validate.length; x++) {
      boolean found = false;
      final char c = validate[x];
      for (int y = 0; y < valid.length; y++) {
        if (c == valid[y]) {
          found = true;
          break;
      if (!found) validate[x] = ' ';
    return String.valueOf(validate);
}I found that 100000 iterations took approx 1400 ms (jdk 1.3). Is there an easy way to make that method any faster?