Java Tutorial: Polymorphism
Method overriding, dynamic dispatch, upcasting and downcasting, and how polymorphism makes code flexible and extensible.
One interface, many forms
Polymorphism means "many forms". A `Shape` reference can point to a `Circle`, `Rectangle`, or `Triangle` — and calling `.area()` on any of them does the right thing automatically.
This is what makes large Java systems extensible — add a new `Shape` subclass and all existing code that works with `Shape` works with it too.
What you'll learn in this Java polymorphism tutorial
This interactive Java tutorial has 5 hands-on exercises. Estimated time: 18 minutes.
- Dynamic dispatch in action — When you call a method through a parent-type reference, Java automatically runs the child's overridden version at runtim…
- Upcasting and downcasting — **Upcasting**: assigning a child type to a parent reference — always safe.
- Polymorphic collections — Store different types in a single collection using the parent type. Process all of them uniformly — each handles itself.
- Overriding equals and hashCode — By default, `equals()` compares references (same memory). Override it to compare content.
- Design a notification system — Final challenge — no starter code.
Java Polymorphism concepts covered
- One interface, many forms