May be modified, the system will verify whether the upgraded application package and the upgraded application package use the same developer signature, and if they are consistent, the application can be upgraded; If it is inconsistent, it will be regarded as an application developed by different developers. Users need to uninstall installed applications before installing new applications. During the uninstallation process, the SavedPreferences of the application in the android system will be deleted to protect the information saved locally by the application from being stolen. This possibility is that it is also risky for developers not to sign by the same person when signing.