Export to google Android Project

when export unity3d to Google Android Project ,there are three files in src folder. they are UnityPlayerActivity UnityPlayerNativeActivity, UnityPlayerProxyActivity; what are these files func or what are they used for?

for example,if i change the android manifest to set mainIntent to be another acitvity,which is originally set to be UnityPlayerNativeActivity. doesn't have any infuluence to the project.