Android timer implementation

Experiment 1: use Java. util. Timer.
Create a timer in onstart (), update the counter every 5 seconds, and start. Java code?

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mTimer = new Timer();        mTimer.schedule(new TimerTask() {                        @Override            public void run() {                 ++mCount;                 mHandler.sendEmptyMessage(0);                            }         }, 5*1000, 5*1000);

When you connect to the USB cable for debugging, you will find that everything works normally and the interface is updated every 5 seconds. Even if you press the power key, it will still be triggered once every 5 seconds.
When the USB cable is unplugged, press the power button to close the screen. After a period of time, it is found that the timer does not continue counting, and the number remains when the power button is disabled.