public class Util {
  private static final String TAG = Util.class.getSimpleName();

  public static Handler handler = new Handler(Looper.getMainLooper());

  public static <T> List<T> asList(T... elements) {
    List<T> result = new LinkedList<>();
    Collections.addAll(result, elements);
    return result;
  }

  public static String join(String[] list, String delimiter) {
    return join(Arrays.asList(list), delimiter);
  }

  public static String join(Collection<String> list, String delimiter) {
    StringBuilder result = new StringBuilder();
    int i = 0;

    for (String item : list) {
      result.append(item);

      if (++i < list.size())
        result.append(delimiter);
    }

    return result.toString();
  }

  public static String join(long[] list, String delimeter) {
    StringBuilder sb = new StringBuilder();

    for (int j=0;j<list.length;j++) {
      if (j != 0) sb.append(delimeter);
      sb.append(list[j]);
    }

    return sb.toString();
  }

  public static ExecutorService newSingleThreadedLifoExecutor() {
    ThreadPoolExecutor executor = new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingLifoQueue<Runnable>());

    executor.execute(new Runnable() {
      @Override
      public void run() {
//        Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
        Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
      }
    });

    return executor;
  }

  public static boolean isEmpty(EncodedStringValue[] value) {
    return value == null || value.length == 0;
  }

  public static boolean isEmpty(EditText value) {
    return value == null || value.getText() == null || TextUtils.isEmpty(value.getText().toString());
  }

  public static CharSequence getBoldedString(String value) {
    SpannableString spanned = new SpannableString(value);
    spanned.setSpan(new StyleSpan(Typeface.BOLD), 0,
                    spanned.length(),
                    Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);

    return spanned;
  }

  public static @NonNull String toIsoString(byte[] bytes) {
    try {
      return new String(bytes, CharacterSets.MIMENAME_ISO_8859_1);
    } catch (UnsupportedEncodingException e) {
      throw new AssertionError("ISO_8859_1 must be supported!");
    }
  }

  public static byte[] toIsoBytes(String isoString) {
    try {
      return isoString.getBytes(CharacterSets.MIMENAME_ISO_8859_1);
    } catch (UnsupportedEncodingException e) {
      throw new AssertionError("ISO_8859_1 must be supported!");
    }
  }

  public static byte[] toUtf8Bytes(String utf8String) {
    try {
      return utf8String.getBytes(CharacterSets.MIMENAME_UTF_8);
    } catch (UnsupportedEncodingException e) {
      throw new AssertionError("UTF_8 must be supported!");
    }
  }

  public static void wait(Object lock, long timeout) {
    try {
      lock.wait(timeout);
    } catch (InterruptedException ie) {
      throw new AssertionError(ie);
    }
  }

  public static void close(InputStream in) {
    try {
      in.close();
    } catch (IOException e) {
      Log.w(TAG, e);
    }
  }

  public static void close(OutputStream out) {
    try {
      out.close();
    } catch (IOException e) {
      Log.w(TAG, e);
    }
  }

  public static long getStreamLength(InputStream in) throws IOException {
    byte[] buffer    = new byte[4096];
    int    totalSize = 0;

    int read;

    while ((read = in.read(buffer)) != -1) {
      totalSize += read;
    }

    return totalSize;
  }

  public static boolean isOwnNumber(Context context, Address address) {
    if (address.isGroup()) return false;
    if (address.isEmail()) return false;

    return TextSecurePreferences.getLocalNumber(context).equals(address.toPhoneString());
  }

  public static byte[] readFully(InputStream in) throws IOException {
    ByteArrayOutputStream bout = new ByteArrayOutputStream();
    byte[] buffer              = new byte[4096];
    int read;

    while ((read = in.read(buffer)) != -1) {
      bout.write(buffer, 0, read);
    }

    in.close();

    return bout.toByteArray();
  }

  public static String readFullyAsString(InputStream in) throws IOException {
    return new String(readFully(in));
  }

  public static long copy(InputStream in, OutputStream out) throws IOException {
    byte[] buffer = new byte[4096];
    int read;
    long total = 0;

    while ((read = in.read(buffer)) != -1) {
      out.write(buffer, 0, read);
      total += read;
    }

    in.close();
    out.close();

    return total;
  }

  public static Optional<Phonenumber.PhoneNumber> getDeviceNumber(Context context) {
    try {
      final String           localNumber = ((TelephonyManager)context.getSystemService(Context.TELEPHONY_SERVICE)).getLine1Number();
      final Optional<String> countryIso  = getSimCountryIso(context);

      if (TextUtils.isEmpty(localNumber)) return Optional.absent();
      if (!countryIso.isPresent())        return Optional.absent();

      return Optional.fromNullable(PhoneNumberUtil.getInstance().parse(localNumber, countryIso.get()));
    } catch (NumberParseException e) {
      Log.w(TAG, e);
      return Optional.absent();
    }
  }

  public static Optional<String> getSimCountryIso(Context context) {
    String simCountryIso = ((TelephonyManager)context.getSystemService(Context.TELEPHONY_SERVICE)).getSimCountryIso();
    return Optional.fromNullable(simCountryIso != null ? simCountryIso.toUpperCase() : null);
  }

  public static <T> List<List<T>> partition(List<T> list, int partitionSize) {
    List<List<T>> results = new LinkedList<>();

    for (int index=0;index<list.size();index+=partitionSize) {
      int subListSize = Math.min(partitionSize, list.size() - index);

      results.add(list.subList(index, index + subListSize));
    }

    return results;
  }

  public static List<String> split(String source, String delimiter) {
    List<String> results = new LinkedList<>();

    if (TextUtils.isEmpty(source)) {
      return results;
    }

    String[] elements = source.split(delimiter);
    Collections.addAll(results, elements);

    return results;
  }

  public static byte[][] split(byte[] input, int firstLength, int secondLength) {
    byte[][] parts = new byte[2][];

    parts[0] = new byte[firstLength];
    System.arraycopy(input, 0, parts[0], 0, firstLength);

    parts[1] = new byte[secondLength];
    System.arraycopy(input, firstLength, parts[1], 0, secondLength);

    return parts;
  }

  public static byte[] combine(byte[]... elements) {
    try {
      ByteArrayOutputStream baos = new ByteArrayOutputStream();

      for (byte[] element : elements) {
        baos.write(element);
      }

      return baos.toByteArray();
    } catch (IOException e) {
      throw new AssertionError(e);
    }
  }

  public static byte[] trim(byte[] input, int length) {
    byte[] result = new byte[length];
    System.arraycopy(input, 0, result, 0, result.length);

    return result;
  }

  @SuppressLint("NewApi")
  public static boolean isDefaultSmsProvider(Context context){
    return (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) ||
      (context.getPackageName().equals(Telephony.Sms.getDefaultSmsPackage(context)));
  }

  public static int getCurrentApkReleaseVersion(Context context) {
    try {
      return context.getPackageManager().getPackageInfo(context.getPackageName(), 0).versionCode;
    } catch (PackageManager.NameNotFoundException e) {
      throw new AssertionError(e);
    }
  }

  public static String getSecret(int size) {
    byte[] secret = getSecretBytes(size);
    return Base64.encodeBytes(secret);
  }

  public static byte[] getSecretBytes(int size) {
    byte[] secret = new byte[size];
    getSecureRandom().nextBytes(secret);
    return secret;
  }

  public static SecureRandom getSecureRandom() {
    try {
      return SecureRandom.getInstance("SHA1PRNG");
    } catch (NoSuchAlgorithmException e) {
      throw new AssertionError(e);
    }
  }

  public static int getDaysTillBuildExpiry() {
    int age = (int)TimeUnit.MILLISECONDS.toDays(System.currentTimeMillis() - BuildConfig.BUILD_TIMESTAMP);
    return 90 - age;
  }

  @TargetApi(VERSION_CODES.LOLLIPOP)
  public static boolean isMmsCapable(Context context) {
    return (VERSION.SDK_INT >= VERSION_CODES.LOLLIPOP) || OutgoingLegacyMmsConnection.isConnectionPossible(context);
  }

  public static boolean isMainThread() {
    return Looper.myLooper() == Looper.getMainLooper();
  }

  public static void assertMainThread() {
    if (!isMainThread()) {
      throw new AssertionError("Main-thread assertion failed.");
    }
  }

  public static void runOnMain(final @NonNull Runnable runnable) {
    if (isMainThread()) runnable.run();
    else                handler.post(runnable);
  }

  public static void runOnMainDelayed(final @NonNull Runnable runnable, long delayMillis) {
    handler.postDelayed(runnable, delayMillis);
  }

  public static void runOnMainSync(final @NonNull Runnable runnable) {
    if (isMainThread()) {
      runnable.run();
    } else {
      final CountDownLatch sync = new CountDownLatch(1);
      runOnMain(new Runnable() {
        @Override public void run() {
          try {
            runnable.run();
          } finally {
            sync.countDown();
          }
        }
      });
      try {
        sync.await();
      } catch (InterruptedException ie) {
        throw new AssertionError(ie);
      }
    }
  }

  public static <T> T getRandomElement(T[] elements) {
    try {
      return elements[SecureRandom.getInstance("SHA1PRNG").nextInt(elements.length)];
    } catch (NoSuchAlgorithmException e) {
      throw new AssertionError(e);
    }
  }

  public static boolean equals(@Nullable Object a, @Nullable Object b) {
    return a == b || (a != null && a.equals(b));
  }

  public static int hashCode(@Nullable Object... objects) {
    return Arrays.hashCode(objects);
  }

  @TargetApi(VERSION_CODES.KITKAT)
  public static boolean isLowMemory(Context context) {
    ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);

    return (VERSION.SDK_INT >= VERSION_CODES.KITKAT && activityManager.isLowRamDevice()) ||
           activityManager.getLargeMemoryClass() <= 64;
  }

  public static int clamp(int value, int min, int max) {
    return Math.min(Math.max(value, min), max);
  }

  public static float clamp(float value, float min, float max) {
    return Math.min(Math.max(value, min), max);
  }

  public static @Nullable String readTextFromClipboard(@NonNull Context context) {
    if (VERSION.SDK_INT >= 11) {
      ClipboardManager clipboardManager = (ClipboardManager)context.getSystemService(Context.CLIPBOARD_SERVICE);

      if (clipboardManager.hasPrimaryClip() && clipboardManager.getPrimaryClip().getItemCount() > 0) {
        return clipboardManager.getPrimaryClip().getItemAt(0).getText().toString();
      } else {
        return null;
      }
    } else {
      android.text.ClipboardManager clipboardManager = (android.text.ClipboardManager)context.getSystemService(Context.CLIPBOARD_SERVICE);

      if (clipboardManager.hasText()) {
        return clipboardManager.getText().toString();
      } else {
        return null;
      }
    }
  }

  public static void writeTextToClipboard(@NonNull Context context, @NonNull String text) {
    if (VERSION.SDK_INT >= 11) {
      ClipboardManager clipboardManager = (ClipboardManager)context.getSystemService(Context.CLIPBOARD_SERVICE);
      clipboardManager.setPrimaryClip(ClipData.newPlainText("Safety numbers", text));
    } else {
      android.text.ClipboardManager clipboardManager = (android.text.ClipboardManager)context.getSystemService(Context.CLIPBOARD_SERVICE);
      clipboardManager.setText(text);
    }
  }

  public static int toIntExact(long value) {
    if ((int)value != value) {
      throw new ArithmeticException("integer overflow");
    }
    return (int)value;
  }

  public static boolean isStringEquals(String first, String second) {
    if (first == null) return second == null;
    return first.equals(second);
  }

  public static boolean isEquals(@Nullable Long first, long second) {
    return first != null && first == second;
  }

  public static String getPrettyFileSize(long sizeBytes) {
    if (sizeBytes <= 0) return "0";

    String[] units       = new String[]{"B", "kB", "MB", "GB", "TB"};
    int      digitGroups = (int) (Math.log10(sizeBytes) / Math.log10(1024));

    return new DecimalFormat("#,##0.#").format(sizeBytes/Math.pow(1024, digitGroups)) + " " + units[digitGroups];
  }
}

其中，同步在主进程中执行任务算是大开眼界了：

在主进程中等待任务完成

其中，话红线的地方表示在这里等待计数器计数完毕才往下面走。不过这样的任务千万不能太耗时，否则会造成ANR。