public String toString() {
      return "CharMatcher.javaLetter()";
    }
  }

  /** Implementation of {@link #javaLetterOrDigit()}. */
  private static final class JavaLetterOrDigit extends CharMatcher {

    static final CharMatcher INSTANCE = new JavaLetterOrDigit();

    @Override
    public boolean matches(char c) {
      return Character.isLetterOrDigit(c);
    }

    @Override