■ 뒤로가기 두번 종료 (BackPressCloseHandler)

backPressCloseHandler = new BackPressCloseHandler(this); // back 이벤트1. BackPressCloseHandler 클래스 생성

import android.app.Activity;
import android.widget.Toast;

public class BackPressCloseHandler {

    private long backKeyPressedTime = 0;
    private Toast toast;

    private Activity activity;

    public BackPressCloseHandler(Activity context) {
        this.activity = context;
    }

    public void onBackPressed() {
        if (System.currentTimeMillis() > backKeyPressedTime + 2000) {
            backKeyPressedTime = System.currentTimeMillis();
            showGuide();
            return;
        }
        if (System.currentTimeMillis() <= backKeyPressedTime + 2000) {
            activity.finish();
            toast.cancel();
        }
    }

    public void showGuide() {
        toast = Toast.makeText(activity,
                "\'뒤로\'버튼을 한번 더 누르시면 종료됩니다.", Toast.LENGTH_SHORT);
        toast.show();
    }
}

2. 적용하려는 클래스에 넣기 ( 빨간 바탕으로된 소스 추가 )

public class Login extends AppCompatActivity {

    private BackPressCloseHandler backPressCloseHandler;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);

        backPressCloseHandler = new BackPressCloseHandler(this); // back 이벤트
    }

    @Override
    public void onBackPressed() {
        //super.onBackPressed();
        backPressCloseHandler.onBackPressed();
    }
}