Private Vs public has nothing to do with security

If people can execute arbitrary code in your app, they can already read your memory, and even if they couldn't they could use java reflection to just turn off the private modifier

Accessibility modifiers are to do with maintainability. If you have internal implementation logic that should be hidden from a consumer you don't want that consumer to have to know about things they shouldn't be changing anyway.

The comic is just about how classnames in java should be in pascal case