Conducive to program upgrade: When the digital certificates of the new program and the old program are the same, the Android system will think that the two programs are different versions of the same program. If the digital certificates of the new program and the old program are different, the Android system thinks that they are different programs and conflict, and requires the new program to change the package name.

It is beneficial to the modular design and development of programs: Android system allows programs with the same digital signature to run in one process, and Android programs will regard them as the same program. Therefore, developers can develop their own programs in the form of modules, and users only need to download the corresponding modules when needed.

You can * * * share data and code among multiple programs through permissions: Android provides a permission granting mechanism based on digital certificates, and applications can * * * share functions or data with other programs to those programs with the same digital certificates. If the protection level of the right is signature, the right can only be granted to programs with the same digital certificate as the package in which the right resides.

Two modes of keystore

Debugging mode: In debugging mode, Android Studio will automatically sign the application with the debugging key, so we can run the program directly.

Release mode: When a program is to be released, the developer needs to sign the apk package with his own digital certificate.