}

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

    static final CharMatcher INSTANCE = new JavaDigit();

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

    @Override
    public String toString() {
      return "CharMatcher.javaDigit()";
    }
  }