Timer倒计时

tv_timer = (TextView) findViewById(R.id.tv_timer);

        final Handler handler=new Handler() {
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                int num = (Integer) msg.obj;
                if(num>0)
                {
                    tv_timer.setText(num+"");
                }else if(num==0)
                {
                    Intent intent=new Intent(SecondActivity.this,LoginActivity.class);
                    startActivity(intent);
                }

            }
        };

        Timer timer=new Timer();
        TimerTask task=new TimerTask() {
            private int num=3;
            @Override
            public void run() {
                num--;
                Message msg = Message.obtain();
                msg.obj=num;
                handler.sendMessage(msg);
            }
        };
        timer.schedule(task,1000,1000);
    }