Four access modifiers and their levels

serial number	access level	access modifier	similar	Same package	Subclass	different packages
1	public	public	Can	Can	Can	Can
2	be protected	protected	Can	Can	Can	Can't
3	default	no access modifier	Can	Can	Can't	Can't
4	private	private	Can	Can't	Can't	Can't

The difference between global variables and local variables
1.
Scope The scope of member variables is in the entire class
. Local variables start from where they are declared and
end where they are located.

2. Initial value
Member variables have an initial value (also called default value, also
called default value). Local variables have no initial value and must be declared and assigned
before use. 3. Modifiers Member variables can use modifiers such as public statc modify

Local variables cannot be
modified with modifiers such as public statc. If you want to use modifiers, you can only use final modifiers

A variable modified by final can only be assigned once, and
its value cannot be modified after the assignment is completed. This variable is called a
constant

final can modify member variables, but when final modifying
member variables, the member variables must be explicitly assigned