安卓:获得普通CountDownTimer的消磨时间？

public class MyCountDownTimer extends CountDownTimer {
    private long startTime;
    private long elapsedTime;

    public MyCountDownTimer(long millisInFuture, long countDownInterval) {
        super(millisInFuture, countDownInterval);
        startTime = System.currentTimeMillis();
    }

    @Override
    public void onTick(long millisUntilFinished) {
        long currentTime = System.currentTimeMillis();
        elapsedTime = currentTime - startTime;
    }

    @Override
    public void onFinish() {
        // 倒计时结束
    }

    public long getElapsedTime() {
        return elapsedTime;
    }
}