Every Android app has a unique application ID that looks like a Java or Kotlin package name, such as com.example.myapp. This ID uniquely identifies your app on the device and in the Google Play Store
android {
defaultConfig {
applicationId "com.example.myapp"
minSdkVersion 15
targetSdkVersion 24
versionCode 1
versionName "1.0"
}
...
}
Although the application ID looks like a traditional Kotlin or Java package name, the naming rules for the application ID are a bit more restrictive:
1. It must have at least two segments (one or more dots).
2. Each segment must start with a letter.
3. All characters must be alphanumeric or an underscore [a-zA-Z0-9_].
When you create a new project in Android Studio, the applicationId is automatically assigned the package name you chose during setup. You can technically toggle the two properties independently from then on, but it is not recommended.
It is recommended that you do the following when setting the application ID:
1. Keep the application ID the same as the namespace. The distinction between the two properties can be a bit confusing, but if you keep them the same, you have nothing to worry about.
2. Don’t change the application ID after you publish your app. If you change it, Google Play Store treats the subsequent upload as a new app.
3. Explicitly define the application ID. If the application ID is not explicitly defined using the applicationId property, it automatically takes on the same value as the namespace. This means that changing the namespace changes the application ID, which is usually not what you want.