Problems in the second day of Android learning

The blogger uses Android Studio, installs the APK into the emulator, runs the first time, uninstalls, and then runs the second time to re-issue the question:
Error type 3
Error: Activity class {com.example.xx.chap2_2/com.example.xx.chap2.FirstActivity} does not exis

Analysis of the problem, I don’t know (to be answered later). Obviously, the uninstallation on the simulator has been finished, the blogger guessed that it should be the simulator problem, there is no such problem when installing the blogger on the real machine.
Modify the package name ApplicationID in the app’s build.gradle and rerun it.

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