Android (Java) Tutorial

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Welcome! This track teaches Android app development using Java. You’ll set up Android Studio, understand the project structure, learn Activities, layouts, resources, and build your first app.

Your First App (Java): “Hello Android”

Step 1: Create a New Project

Open Android Studio, go to File → New → New Project. Choose Empty Activity, give your project a name (HelloAndroid), set the language to Java, and choose a Minimum SDK (API 21 is recommended). After you click Finish, Android Studio will generate the starter files for you.

Step 2: Design the Layout

The layout is written in XML. It defines how your screen looks. Here, we’re placing a TextView (to show text) and a Button.

<!-- XML layout for the main screen -->
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    android:padding="16dp">

    <TextView
        android:id="@+id/tvMessage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello Android!"
        android:textSize="22sp"/>

    <Button
        android:id="@+id/btnClick"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click Me"
        android:layout_marginTop="12dp"/>

</LinearLayout>

Explanation: - LinearLayout arranges items vertically. - TextView shows static text. - Button lets users interact by clicking.

Step 3: Add Java Code

Now let’s connect the layout with logic. In MainActivity.java, we reference the button and text, then set a click listener to change the text and show a Toast message.

public class MainActivity extends AppCompatActivity {

    private TextView tvMessage;
    private Button btnClick;

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

        tvMessage = findViewById(R.id.tvMessage);
        btnClick  = findViewById(R.id.btnClick);

        btnClick.setOnClickListener(new View.OnClickListener() {
            @Override 
            public void onClick(View v) {
                tvMessage.setText("Welcome to Android with Java!");
                Toast.makeText(MainActivity.this, "Button Clicked", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

Explanation: - findViewById() connects UI elements to Java code. - setOnClickListener() runs code when the button is clicked. - Toast is a small popup message.

Step 4: Declare in Manifest

<application
    android:theme="@style/Theme.AppCompat.Light.NoActionBar">

    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

</application>

The AndroidManifest.xml declares all components of your app. Here we mark MainActivity as the launcher activity with an intent filter.

Step 5: Gradle Setup

android {
    compileSdkVersion 34

    defaultConfig {
        applicationId "com.example.helloandroid"
        minSdkVersion 21
        targetSdkVersion 34
        versionCode 1
        versionName "1.0"
    }
}

Explanation: - compileSdkVersion tells Gradle which Android APIs you can use. - minSdkVersion is the oldest Android version your app supports. - targetSdkVersion is the version you’ve tested your app against.

Step 6: Run Your App

Start an emulator from AVD Manager, or connect a real Android device.
Click the green ▶ Run button in Android Studio.
Tap the button → text changes and a Toast appears 🎉

Tip: If you see the text change and Toast on button click, your setup is correct!

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