Encapsulation
Encapsulation refer to when we define a class, we need to Privatizing attributes in a class, which is, use private to modify.
private attribute can only be accessed in the class.
if outer want to access private attribute, we need to provide public method. such as set() or get().
Package
包将类封装到不同的目录中 Packages encapsulate classes in different directories
同一个包中的类,可以直接用类名访问 Classes in the same package can be accessed directly with the class name
不同包中的类,可以使用包名.类名 访问 Classes in different packages can be accessed using package name. class name or use import to import package.

Access control permissions

参考: https://blog.youkuaiyun.com/weixin_50849959/article/details/116595077