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

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

    static final CharMatcher INSTANCE = new JavaUpperCase();

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

    @Override