JAVA android 点击两次返回键退出

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    
    @Override
    public void onBackPressed() {
        Log.d("onBackPressed", "touch BackPressed");
        twoTimesToExit();
    }

    private long exitTime;
    
    public void twoTimesToExit() {
        if ((System.currentTimeMillis() - exitTime) > 2000) {
            Toast.makeText(this, "再按一次退出", Toast.LENGTH_SHORT).show();
            exitTime = System.currentTimeMillis();
        } else {
            this.finish();
            System.exit(0);
        }
    }
}