Inheritance: extends, super, and Method Overriding

extends says is-a

public class Manager extends Employee declares that every Manager is an Employee. The subclass inherits all public methods of the superclass. It does not inherit constructors, and although every subclass object still carries the superclass private instance variables, it cannot touch them by name — it must go through the superclass accessors and mutators.

Constructors run outward-in

The first statement of every subclass constructor is a call to a superclass constructor. If you write super(...) explicitly, that one runs; if you write nothing, Java inserts super() with no arguments. So if the superclass has no no-argument constructor and you forget the explicit super(...), the code does not compile. Execution order is therefore superclass constructor first, then the subclass constructor body.

Overriding versus overloading

Overriding replaces an inherited method: same name, same parameter list, in a subclass. Overloading adds a new method: same name, different parameter list, usually in the same class. Change a parameter type by accident and you have overloaded rather than overridden — the superclass version still runs, and nothing warns you.

Inside an override, super.methodName(args) calls the superclass version, which is the standard way to say do everything the parent did, then add my part.