Every Android app has a unique application ID that looks like a Java package name, such as com.example.myapp. This ID uniquely identifies your app on the device and in Google Play Store. If you want to upload a new version of your app, the application ID (and the certificate you sign it with) must be the same as the original artifact—if you change the application ID, Google Play Store treats the upload as a completely different app. So once you publish your app, you should never change the application ID.

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