Many Android developers don't understand the function of APK signature. In fact, APK signature has two main uses: 1. Some different permissions can be obtained by using a special key signature. 2. If APK uses a key signature, the file signed by another key will not be able to install or overwrite the old version when it is published, which can prevent your installed application from being overwritten or replaced by a malicious third party. At present, Google's attitude and strategy in Android system is also non-profit, which is essentially different from Symbian's signboard. However, the APK file that we installed from the development environment to the mobile phone using Eclipse+ADT plug-in already contains the debugging signature file of ADT plug-in, so it was not installed, but the final released version needs its own key to sign.