Android Project Structure (Java)

Android Studio organizes your app into modules and folders so code, resources, and build settings stay clean. This page explains each part so you always know where to add files and why they matter.

Bird’s-Eye View

Quick Tree

# Important paths you will use most of the time
HelloAndroid/
  settings.gradle
  build.gradle        // Project-level
  gradle.properties
  app/
    build.gradle      // Module-level
    src/
      main/
        AndroidManifest.xml
        java/com/example/helloandroid/MainActivity.java
        res/
          layout/activity_main.xml
          values/strings.xml, colors.xml, styles.xml
          drawable/ (shapes, vectors), mipmap-*/ (app icons)
          xml/ (config XMLs, e.g., file_paths.xml)
      androidTest/      // UI tests
      test/             // Unit tests

Project-Level Files

File	Purpose
settings.gradle	Lists included modules. Most projects start with :app.
build.gradle (Project)	Global build setup (Gradle plugin version, repositories for all modules).
gradle.properties	Global build flags and JVM options (e.g., org.gradle.jvmargs).

// settings.gradle
include ':app'

// build.gradle (Project)
buildscript {
  repositories { google(); mavenCentral() }
  dependencies {
    classpath 'com.android.tools.build:gradle:8.4.1'
  }
}

Module: app/

The app module contains everything that gets packaged into your APK/AAB.

app/build.gradle (Module)

plugins { id 'com.android.application' }

android {
  namespace "com.example.helloandroid"
  compileSdk 34

  defaultConfig {
    applicationId "com.example.helloandroid"
    minSdk 21
    targetSdk 34
    versionCode 1
    versionName "1.0"
  }

  buildTypes {
    release {
      minifyEnabled false
      proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
  }
}

dependencies {
  implementation 'androidx.appcompat:appcompat:1.7.0'
  implementation 'com.google.android.material:material:1.12.0'
}

src/main/AndroidManifest.xml

Declares app components (Activities/Services), permissions, and metadata. It also marks your launcher activity.

src/main/java/

Source code in package folders (e.g., com.example.helloandroid). Typical structure:

• ui (activities/fragments/adapters)
• data (repositories, models, DB)
• network (API interfaces)
• util (helpers)

src/main/res/ (Resources)

Folder	Use	Examples
layout/	UI screens in XML	activity_main.xml, item_row.xml
values/	Strings, colors, styles, dimens	strings.xml, colors.xml, styles.xml
drawable/	Images & shapes (png/xml/vector)	bg_button.xml, ic_logo.xml
mipmap-*/	App launcher icons (various densities)	mipmap-xxxhdpi/ic_launcher.png
xml/	Config XMLs	file_paths.xml, backup_rules.xml
menu/	Toolbar/overflow menus	main_menu.xml
anim/, animator/	View and property animations	fade_in.xml
font/	Font resources	poppins_regular.ttf

Assets & Raw

• src/main/assets/: arbitrary files you read with AssetManager (e.g., HTML, JSON).
• src/main/res/raw/: raw resources accessed via R.raw.file_name (e.g., audio, SQL).

How R Class Works

Android generates R.java so you can reference resources in type-safe ways: R.layout.activity_main, R.id.btnClick, R.string.app_name. Names come from file names and android:id attributes.

// Example usage in Activity
TextView tv = findViewById(R.id.tvMessage);
setContentView(R.layout.activity_main);
setTitle(R.string.app_name);

Build Variants (debug/release) & Flavors

You can override code/resources per build type or flavor.

# Example folders
app/src/debug/AndroidManifest.xml
app/src/release/AndroidManifest.xml
app/src/free/res/values/strings.xml
app/src/pro/res/values/strings.xml

// app/build.gradle (flavor example)
android {
  flavorDimensions "tier"
  productFlavors {
    free { dimension "tier" }
    pro  { dimension "tier" }
  }
}

Density & Qualifiers

Provide alternatives for different screens/regions:

• Density: drawable-hdpi/, -xhdpi/, -xxhdpi/
• Language: values-hi/strings.xml
• Night: values-night/colors.xml
• Layout size/orientation: layout-land/, layout-sw600dp/

Where Do I Put…?

Thing	Folder	Reference
Screen UI	res/layout/	R.layout.activity_main
Static text	res/values/strings.xml	R.string.hello_text
Shapes/vector icons	res/drawable/	R.drawable.bg_button
App icon	res/mipmap-*/	Configured in manifest
Fonts	res/font/	@font/poppins_regular
Config XML	res/xml/	R.xml.file_paths
JSON/HTML to read	assets/	AssetManager
Audio/video raw	res/raw/	R.raw.beep

Common Pitfalls

Hands-On: Add a Shape Background

1. Create res/drawable/bg_rounded_button.xml:

<!-- res/drawable/bg_rounded_button.xml -->
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle">
  <solid android:color="@color/purple_500"/>
  <corners android:radius=8dp"/>
  <padding android:left="12dp" android:top="8dp"
           android:right="12dp" android:bottom="8dp"/>
</shape>

2. Apply in activity_main.xml Button: android:background="@drawable/bg_rounded_button"
3. Run the app and see the styled button.

Troubleshooting