用android studio编写一个计时器

以下是一个简单的Android Studio计时器的示例代码：

public class MainActivity extends AppCompatActivity {

    private TextView mTextView;
    private Button mButtonStart;
    private Button mButtonStop;
    private Switch mSwitch;    private CountDownTimer mCountDownTimer;
    private boolean mTimerRunning;
    private long mTimeLeftInMillis = 600000; // 10分钟
    private long mEndTime;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mTextView = findViewById(R.id.text_view_countdown);
        mButtonStart = findViewById(R.id.button_start);
        mButtonStop = findViewById(R.id.button_stop);        mSwitch = findViewById(R.id.switch_timer);

        mButtonStart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startTimer();
            }
        });

        mButtonStop.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                stopTimer();
            }
        });

        mSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                if (isChecked) {
                    mTimeLeftInMillis = 300000; // 5分钟
                } else {
                    mTimeLeftInMillis = 600000; // 10分钟
                }
                updateCountDownText();
            }
        });

        updateCountDownText();
    }

    private void startTimer() {
        mEndTime = System.currentTimeMillis() + mTimeLeftInMillis;

        mCountDownTimer = new CountDownTimer(mTimeLeftInMillis, 1000) {
            @Override
            public void onTick(long millisUntilFinished) {
                mTimeLeftInMillis = millisUntilFinished;
                updateCountDownText();
            }

            @Override
            public void onFinish() {
                mTimerRunning = false;
                mButtonStart.setVisibility(View.VISIBLE);
                mButtonStop.setVisibility(View.INVISIBLE);
            }
        }.start();

        mTimerRunning = true;
        mButtonStart.setVisibility(View.INVISIBLE);
        mButtonStop.setVisibility(View.VISIBLE);
    }

    private void stopTimer() {
        mCountDownTimer.cancel();
        mTimerRunning = false;
        mButtonStart.setVisibility(View.VISIBLE);
        mButtonStop.setVisibility(View.INVISIBLE);
    }

    private void updateCountDownText() {
        int minutes = (int) (mTimeLeftInMillis / 1000) / 60;
        int seconds = (int) (mTimeLeftInMillis / 1000) % 60;

        String timeLeftFormatted = String.format(Locale.getDefault(), "%02d:%02d", minutes, seconds);

        mTextView.setText(timeLeftFormatted);
    }
}

这个计时器包括一个文本视图，两个按钮和一个开关。用户可以选择计时器的时间长度，然后按下“开始”按钮启动计时器。计时器将在指定的时间内倒计时，并在计时结束时停止。用户还可以按下“停止”按钮手动停止计时器。