计算活动开始后经过了多少秒[关闭]

public class MainActivity extends AppCompatActivity {

    private TextView mTimeTextView;
    private Button mTimeButton;
    private Calendar mStartTime;

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

        mStartTime = Calendar.getInstance();

        mTimeTextView = (TextView) findViewById(R.id.time_text_view);
        mTimeButton = (Button) findViewById(R.id.time_button);

        mTimeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Calendar nowTime = Calendar.getInstance();
                long secs = (nowTime.getTimeInMillis() - mStartTime.getTimeInMillis())/1000;
                mTimeTextView.setText(String.valueOf(secs));
            }
        });
    }
}