[Java] access control operator privileges Summary

Modifiers	Inner classes	The same package (the same folder)	Subclass (does not require the same package)	The remaining positions	Suitable
default (without any modifiers)	✅	✅	❌	❌	Class (interface), methods, properties
public	✅	✅	✅	✅	Ditto
private	✅	❌	❌	❌	Methods, properties
protected	✅	✅	✅	❌	Ditto