Where is the jar file for Android located? (Just out of curiosity)

I am developing an android api android application .

Now I would like to find out where the actual jar is located (and not the android.jar 'Api jar file included in the project) containing the execution body, i.e. java file implementation implementation "android.jar.

I searched a lot in the Android sdk installation directory, but no such jar file was found. Is there any jar file for this purpose? If not, how does the android virtual device execute the source code?

Thank.