JAVA_HOME("java.home"),

  /** Java Virtual Machine specification version. */
  JAVA_VM_SPECIFICATION_VERSION("java.vm.specification.version"),

  /** Java Virtual Machine specification vendor. */
  JAVA_VM_SPECIFICATION_VENDOR("java.vm.specification.vendor"),

  /** Java Virtual Machine specification name. */
  JAVA_VM_SPECIFICATION_NAME("java.vm.specification.name"),

  /** Java Virtual Machine implementation version. */

   * want to accept ASCII digits only, you can use something like {@code
   * CharMatcher.ascii().matchesAllOf(ipString)}.
   *
   * <p>The scope ID is validated against the interfaces on the machine, which requires permissions
   * under Android.
   *
   * <p><b>Android users on API >= 29:</b> Prefer {@code InetAddresses.parseNumericAddress}.
   *

   * want to accept ASCII digits only, you can use something like {@code
   * CharMatcher.ascii().matchesAllOf(ipString)}.
   *
   * <p>The scope ID is validated against the interfaces on the machine, which requires permissions
   * under Android.
   *
   * <p><b>Android users on API >= 29:</b> Prefer {@code InetAddresses.parseNumericAddress}.
   *

   *
   * @since 8.0
   */
  public static final byte NUL = 0;

  /**
   * Start of Heading: A communication control character used at the beginning of a sequence of
   * characters which constitute a machine-sensible address or routing information. Such a sequence
   * is referred to as the "heading." An STX character has the effect of terminating a heading.
   *
   * @since 8.0
   */
  public static final byte SOH = 1;

   * @throws IllegalCharsetNameException if a charset value is present, but illegal
   * @throws UnsupportedCharsetException if a charset value is present, but no support is available
   *     in this instance of the Java virtual machine
   */
  public Optional<Charset> charset() {
    // racy single-check idiom, this is safe because Optional is immutable.
    Optional<Charset> local = parsedCharset;
    if (local == null) {

    }
  }


  @J2ktIncompatible // slow enough to cause flakiness
  @GwtIncompatible // far too slow
  public void testSqrtOfPerfectSquareAsDoubleIsPerfect() {
    // This takes just over a minute on my machine.
    for (long n = 0; n <= LongMath.FLOOR_SQRT_MAX_LONG; n++) {
      long actual = (long) Math.sqrt((double) (n * n));
      assertTrue(actual == n);
    }
  }

     *
     * @param hook The shutdown hook to add.
     */
    public void addShutdownHook(final Runnable hook) {
        shutdownHookList.add(hook);
    }

    /**
     * Gets the hostname of the local machine.
     *
     * @return The hostname.
     */
    public String getHostname() {
        final Map<String, String> env = getEnvMap();
        if (env.containsKey("COMPUTERNAME")) {

    if (parent == null) {
      /*
       * The given directory is a filesystem root. All zero of its ancestors exist. This doesn't
       * mean that the root itself exists -- consider x:\ on a Windows machine without such a drive
       * -- or even that the caller can create it, but this method makes no such guarantees even for
       * non-root files.
       */
      return;
    }
    parent.mkdirs();

    if (parent == null) {
      /*
       * The given directory is a filesystem root. All zero of its ancestors exist. This doesn't
       * mean that the root itself exists -- consider x:\ on a Windows machine without such a drive
       * -- or even that the caller can create it, but this method makes no such guarantees even for
       * non-root files.
       */
      return;
    }
    parent.mkdirs();

   * @throws IllegalCharsetNameException if a charset value is present, but illegal
   * @throws UnsupportedCharsetException if a charset value is present, but no support is available
   *     in this instance of the Java virtual machine
   */
  public Optional<Charset> charset() {
    // racy single-check idiom, this is safe because Optional is immutable.
    Optional<Charset> local = parsedCharset;
    if (local == null) {