Which access modifier restricts access to the class or subclass only?

The access modifier that restricts access to a class or subclass only is known as 'protected.' This modifier allows members (variables and methods) of a class to be accessed only within that class and by subclasses (derived classes).

The use of protected access is particularly useful in object-oriented programming when you want to limit the visibility of certain class members while still allowing subclasses to inherit and utilize them. By doing so, it promotes encapsulation, allowing a class to protect its internal structure while still providing a way for derivatives to interact with or manipulate specific features.

In contrast, the public access modifier allows complete access from any other code beyond the class itself, while private restricts access entirely to the owning class. The static keyword, on the other hand, is not an access modifier at all but rather indicates that a member belongs to the class itself rather than instances of the class.