倒计时

方法一

Timer与TimerTask（Java实现）

public class timerTask extends Activity{  
 
    private int recLen = 11;  
    private TextView txtView;  
    Timer timer = new Timer();  
 
    public void onCreate(Bundle savedInstanceState){  
        super.onCreate(savedInstanceState);  
          
        setContentView(R.layout.timertask);  
        txtView = (TextView)findViewById(R.id.txttime);  
          
        timer.schedule(task, 1000, 1000);       // timeTask  
    }     
 
    TimerTask task = new TimerTask() {  
        @Override  
        public void run() {  
 
            runOnUiThread(new Runnable() {      // UI thread  
                @Override  
                public void run() {  
                    recLen--;  
                    txtView.setText(""+recLen);  
                    if(recLen < 0){  
                        timer.cancel();  
                        txtView.setVisibility(View.GONE);  
                    }  
                }  
            });  
        }  
    };  
}  

方法二 
TimerTask与Handler（不用Timer的改进型）

public class timerTask extends Activity{  
    private int recLen = 11;  
    private TextView txtView;  
    Timer timer = new Timer();  
 
    public void onCreate(Bundle savedInstanceState){  
        super.onCreate(savedInstanceState);  
 
        setContentView(R.layout.timertask);  
        txtView = (TextView)findViewById(R.id.txttime);  
 
        timer.schedule(task, 1000, 1000);       // timeTask  
    }     
 
    final Handler handler = new Handler(){  
        @Override  
        public void handleMessage(Message msg){  
            switch (msg.what) {  
            case 1:  
                txtView.setText(""+recLen);  
                if(recLen < 0){  
                    timer.cancel();  
                    txtView.setVisibility(View.GONE);  
                }  
            }  
        }  
    };  
 
    TimerTask task = new TimerTask() {  
        @Override  
        public void run() {  
            recLen--;  
            Message message = new Message();  
            message.what = 1;  
            handler.sendMessage(message);  
        }  
    };  
}  

方法三

Handler与Message（不用TimerTask）

public class timerTask extends Activity{  
    private int recLen = 11;  
    private TextView txtView;  
 
    public void onCreate(Bundle savedInstanceState) {    
        super.onCreate(savedInstanceState);    
 
        setContentView(R.layout.timertask);   
        txtView = (TextView)findViewById(R.id.txttime);  
 
        Message message = handler.obtainMessage(1);     // Message  
        handler.sendMessageDelayed(message, 1000);  
    }    
 
    final Handler handler = new Handler(){  
 
        public void handleMessage(Message msg){         // handle message  
            switch (msg.what) {  
            case 1:  
                recLen--;  
                txtView.setText("" + recLen);  
 
                if(recLen > 0){  
                    Message message = handler.obtainMessage(1);  
                    handler.sendMessageDelayed(message, 1000);      // send message  
                }else{  
                    txtView.setVisibility(View.GONE);  
                }  
            }  
 
            super.handleMessage(msg);  
        }  
    };  
}  

方法四 

Handler与Thread（不占用UI线程）

public class timerTask extends Activity{  
    private int recLen = 0;  
    private TextView txtView;  
 
    public void onCreate(Bundle savedInstanceState){  
        super.onCreate(savedInstanceState);  
 
        setContentView(R.layout.timertask);  
        txtView = (TextView)findViewById(R.id.txttime);  
          
        new Thread(new MyThread()).start();         // start thread  
    }     
 
    final Handler handler = new Handler(){          // handle  
        public void handleMessage(Message msg){  
            switch (msg.what) {  
            case 1:  
                recLen++;  
                txtView.setText("" + recLen);  
            }  
            super.handleMessage(msg);  
        }  
    };  
 
    public class MyThread implements Runnable{      // thread  
        @Override  
        public void run(){  
            while(true){  
                try{  
                    Thread.sleep(1000);     // sleep 1000ms  
                    Message message = new Message();  
                    message.what = 1;  
                    handler.sendMessage(message);  
                }catch (Exception e) {  
                }  
   

方法五

Handler与Runnable（最简单型）  

public class timerTask extends Activity{  
    private int recLen = 0;  
    private TextView txtView;  
 
    public void onCreate(Bundle savedInstanceState){  
        super.onCreate(savedInstanceState);  
 
        setContentView(R.layout.timertask);  
        txtView = (TextView)findViewById(R.id.txttime);  
          
        handler.postDelayed(runnable, 1000);  
    }     
 
    Handler handler = new Handler();  
    Runnable runnable = new Runnable() {  
        @Override  
        public void run() {  
            recLen++;  
            txtView.setText("" + recLen);  
            handler.postDelayed(this, 1000);  
        }  
    };  
}  

计时与倒计时 
方法1，方法2和方法3，都是倒计时 
方法4，方法5，都是计时 
计时和倒计时，都可使用上述方法实现（代码稍加改动） 

UI线程比较 
方法1，方法2和方法3，都是在UI线程实现的计时； 
方法4和方法5，是另开Runnable线程实现计时 

实现方式比较 
方法1，采用的是Java实现，即Timer和TimerTask方式； 
其它四种方法，都采用了Handler消息处理 

推荐使用 
如果对UI线程交互要求不很高，可以选择方法2和方法3 
如果考虑到UI线程阻塞，严重影响到用户体验，推荐使用方法4，另起线程单独用于计时和其它的逻辑处理 
方法5，综合了前几种方法的优点，是最简的