#build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "gokisoft.j2010g"
        minSdkVersion 19
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:2.0.4'
}

#AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="gokisoft.j2010g">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".TestActivity"></activity>
    </application>

</manifest>

#MainActivity.java

package gokisoft.j2010g;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    //Mapping object trong XML sang Java
    EditText edEmail, edPassword;
    Button btnSave, btnReset, btnStart;

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

        //Mapping object java & component trong xml
        edEmail = findViewById(R.id.am_ed_email);
        edPassword = findViewById(R.id.am_ed_password);
        btnSave = findViewById(R.id.am_btn_save);
        btnReset = findViewById(R.id.am_btn_reset);
        btnStart = findViewById(R.id.am_btn_start);

        //Bat su kien khi nguoi dung click vao button save & reset
        btnSave.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //noi xu ly code -> khi click vao button save
                String email = edEmail.getText().toString();
                String pwd = edPassword.getText().toString();

                Log.d("MainActivity", email);
                Log.d(MainActivity.class.getName(), pwd);

                //Gia su neu email: aptech@com & pwd: 123 => show message: Login success!
                //Show message: Login failed.
                if(email.equals("aptech@com") && pwd.equals("123")) {
                    //login success
                    Toast.makeText(MainActivity.this, "Login success", Toast.LENGTH_SHORT).show();
                } else {
                    //login failed
                    Toast.makeText(MainActivity.this, "Login failed", Toast.LENGTH_SHORT).show();
                }
            }
        });

        btnReset.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //noi xu ly code -> khi click vao button reset
                edEmail.setText("");
                edPassword.setText("");
            }
        });

        btnStart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent in = new Intent(MainActivity.this, TestActivity.class);
                startActivity(in);
            }
        });
    }
}

#TestActivity.java

package gokisoft.j2010g;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class TestActivity extends AppCompatActivity {

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

#activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="gokisoft.j2010g.MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Login"
        android:textAlignment="center"
        android:textColor="@color/colorRed"
        android:textSize="25dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:textSize="16dp"
        android:text="Email:" />

    <EditText
        android:id="@+id/am_ed_email"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:padding="10dp"
        android:hint="Enter email"
        android:textSize="16dp"
        android:inputType="textPersonName"
        android:text="" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="16dp"
        android:padding="10dp"
        android:text="Password:" />

    <EditText
        android:id="@+id/am_ed_password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:textSize="16dp"
        android:padding="10dp"
        android:hint="Enter password"
        android:inputType="textPersonName"
        android:text="" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:weightSum="2"
        android:orientation="horizontal">

        <Button
            android:id="@+id/am_btn_save"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Save Data" />

        <Button
            android:id="@+id/am_btn_reset"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Reset Data" />
    </LinearLayout>

    <Button
        android:id="@+id/am_btn_start"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Start Test Activity" />

</LinearLayout>

#activity_test.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="gokisoft.j2010g.TestActivity">

    <TextView
        android:id="@+id/textView2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="50dp"
        android:textColor="@color/colorRed"
        android:textAlignment="center"
        android:text="Welcome to learn Android" />
</LinearLayout>