好吧……我承认很尴尬……

但毕竟作为开端，还是将这个贴出来，以后一定写出厉害的！

package myapplication.nomasp.com.timer;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.TextView;import java.util.Timer;import java.util.TimerTask;public class MainActivity extends Activity implements View.OnClickListener {
         private EditText etInputNum,etOutputNum;    private Button btnGetNum,btnStartCount,btnStopCount;    private TextView tvOutputNum;    private  int i=0;    private Timer timer=null;    private TimerTask task=null;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initView();    }    private void initView(){        etInputNum=(EditText)findViewById(R.id.etInputNum);        btnGetNum=(Button)findViewById(R.id.btnGetNum);        btnStartCount=(Button)findViewById(R.id.btnStartCount);        btnStopCount=(Button)findViewById(R.id.btnStopCount);        tvOutputNum=(TextView)findViewById(R.id.tvOutputNum);        btnGetNum.setOnClickListener(this);        btnStartCount.setOnClickListener(this);        btnStopCount.setOnClickListener(this);    }    @Override    public void onClick(View v)    {        switch (v.getId())        {            case R.id.btnGetNum:                tvOutputNum.setText(etInputNum.getText().toString());                i=Integer.parseInt(etInputNum.getText().toString());                break;            case R.id.btnStartCount:                startTime();                break;            case R.id.btnStopCount:                stopTime();                break;            default:                break;        }    }    private Handler mHandler=new Handler(){        public void handleMessage(Message msg){            tvOutputNum.setText(msg.arg1+"");            startTime();        };    };    public void startTime(){        timer=new Timer();        task =new TimerTask() {            @Override            public void run() {                i--;                Message message=mHandler.obtainMessage();                message.arg1=i;                mHandler.sendMessage(message);            }        };        timer.schedule(task,1000);    }    public void stopTime(){        timer.cancel();    }}

加油！