Introduction to Android (Java)

In this introduction, you’ll understand what Android is, how apps are structured, and the core building blocks (Activities, Services, Broadcast Receivers, Content Providers). We’ll also walk through Intents, Lifecycle, Permissions, and how apps are built and packaged.

What is Android?

Android App Components

These components are declared in AndroidManifest.xml. The OS creates/destroys them as needed.

AndroidManifest.xml (minimal example)

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapp">

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

</manifest>

Intents & Navigation

An Intent is a message to request an action from another component (start an Activity, Service, or deliver a broadcast).

Example: Start a new Activity

Intent intent = new Intent(CurrentActivity.this, DetailActivity.class);
startActivity(intent);

Activity Lifecycle (High Level)

The system calls lifecycle methods as the Activity appears/disappears:

Project Structure (Quick Map)

Permissions (Runtime Model)

Some features need user permission (e.g., camera, location). From Android 6.0 (API 23+), you request them at runtime.

// In AndroidManifest.xml
<uses-permission android:name="android.permission.CAMERA" />

// In Activity (Java) – request at runtime
if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
        != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(this,
        new String[]{Manifest.permission.CAMERA}, 101);
}

Build Output: APK vs AAB

Gradle (Build System)

Gradle manages builds, dependencies, flavors, and signing.

android {
    compileSdkVersion 34

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

High-Level Development Flow

FAQs