对您的示例的简单修复是：

handler = new Handler();
final Runnable r = new Runnable() {
    public void run() {
        tv.append("Hello World");
        handler.postDelayed(this, 1000);
handler.postDelayed(r, 1000);

或者我们可以使用普通线程(例如，使用原始Runner)：

Thread thread = new Thread() {
    @Override
    public void run() {
        try {
            while(true) {
                sleep(1000);
                handler.post(this);
        } catch (InterruptedException e) {
            e.printStackTrace();
thread.start();

您可以将runnable对象看作是可以发送到消息队列以供执行的命令，而handler仅仅是用于发送该命令的辅助对象。

更多细节在这里 http://developer.android.com/reference/android/os/Handler.html

一个有趣的例子是，您可以连续看到计数器/秒表在单独的线程中运行。还显示了GPS定位。而主活动用户界面线程已经存在。

摘录：

try {    
    cnt++; scnt++;
    now=System.currentTimeMillis();
    r=rand.nextInt(6); r++;    
    loc=lm.getLastKnownLocation(best);    
    if(loc!=null) { 
        lat=loc.getLatitude();
        lng=loc.getLongitude(); 
    Thread.sleep(100); 
    handler.sendMessage(handler.obtainMessage());
} catch (InterruptedException e) {   
    Toast.makeText(this, "Error="+e.toString(), Toast.LENGTH_LONG).show();
}

要查看代码，请参阅此处：

Thread example displaying GPS Location and Current Time runnable alongside main-activity's User Interface Thread

现在在Kotlin中，你可以这样运行线程：

class SimpleRunnable: Runnable {
    public override fun run() {
        println("${Thread.currentThread()} has run.")
fun main(args: Array<String>) {
    val thread = SimpleThread()
    thread.start() // Will output: Thread[Thread-0,5,main] has run.
    val runnable = SimpleRunnable()
    val thread1 = Thread(runnable)
    thread1.start() // Will output: Thread[Thread-1,5,main] has run
}

Kotlin

private lateinit var runnable: Runnable
override fun onCreate(savedInstanceState: Bundle?) {
    val handler = Handler()
    runnable = Runnable {
        // do your work
        handler.postDelayed(runnable, 2000)
    handler.postDelayed(runnable, 2000)
}

Java

Runnable runnable;
Handler handler;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    handler = new Handler();
    runnable = new Runnable() {
        @Override
        public void run() {
            // do your work
            handler.postDelayed(this, 1000);