뒤로가기 두번 눌러 앱 종료

public class MainActivity extends AppCompatActivity {

    private long backBtnTime = 0;

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


    @Override
    public void onBackPressed() {
        long curTime = System.currentTimeMillis();
        long gapTime = curTime - backBtnTime;

        if(0 <= gapTime && 2000 >= gapTime) {
            super.onBackPressed();
        }
        else {
            backBtnTime = curTime;
            Toast.makeText(this, "한번 더 누르면 종료됩니다.",Toast.LENGTH_SHORT).show();
        }


    }
}

https://www.youtube.com/watch?v=3jiQGrjOgMM

https://github.com/hongdroid94/23_BackButton