link

https://www.geeksforgeeks.org/android-android-apps-file-structure/

https://www.sourcecodester.com/android/11968/android-simple-login-application-beginners.html

https://developer.android.com/codelabs/build-your-first-android-app#2

https://github.com/mohjacksi/AndroidOrderingSystemApp?fbclid=IwAR2h_sxcG53Lfecb6EvvAiAbDcdZk7JWygyEqtraz61Ut8iUexDagALnch0

https://www.studocu.com/vn/document/truong-dai-hoc-su-pham-ky-thuat-thanh-pho-ho-chi-minh/lap-trinh-tren-windows/bai-tap-lon-lap-trinh-ung-dung-dat-do-an-nho/27339430?fbclid=IwAR0Ubfmc8HTnAMpxT3hCLyZAhDLHb46IzXoiu2zbkEC6A0YU2hURrPFLHZ8

https://www.youtube.com/watch?v=9nWcPPHBzMk

#button to go to another activity
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

##examp (sau tối ưu)

package com.example.myapplication;

import android.content.Intent;
import android.os.Bundle;
import android.widget.Button;

import androidx.appcompat.app.AppCompatActivity;


public class MainActivity extends AppCompatActivity {



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

        final Button button = (Button) findViewById(R.id.button2);

        button.setOnClickListener(view -> {

            Intent i = new Intent(getApplicationContext(),IntroActivity.class);
            startActivity(i);

        });
    }
}