ComparisonDifficulty: Intermediate1 min

Overriding vs Overloading

Two words a letter apart, decided at different times, and a method that is never called if you confuse them.

Overriding is a subclass replacing a parent method's body with a method of the same name and the same parameter list; which body runs is decided by the object while the program runs. Overloading is adding another method with the same name and a different parameter list; the compiler picks between them.

Overriding against overloading, on where, what and when
Compared on	Overriding	Overloading
Where the two methods live	Parent and subclass	Anywhere, usually one class
Name	The same	The same
Parameter list	The same	Must differ
Decided by	The runtime type of the object	The compiler, from declared types
Decided when	While the program runs	While it is compiled

java

class Customer {
    String label() { return "To: " + name; }
}

class PremiumCustomer extends Customer {
    @Override
    String label() { return "To our valued customer: " + name; }

    String label(String prefix) { return prefix + name; }
}

line 7 overrides; line 9 overloads

Line 9 does not replace anything. It is a second method with the same name and a different parameter list, so a PremiumCustomer now has two label methods and the compiler picks between them by what you pass.

The decision rule. Write @Override on every method you intend to override. It is not decoration: the compiler checks that something up the hierarchy really has that exact signature, and it fails the build when a typo or a changed parameter type has quietly turned an override into an overload.

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