Java OOP Compiler

Object-Oriented Programming is the heart of Java. These runnable examples cover the four pillars — edit them in the browser to see polymorphism and encapsulation in action.

Run Java OOP Compiler examples in the Java compiler

Examples included

Run the class object example
Run the inheritance example
Run the polymorphism example
Run the interface example
Run the encapsulation example

Practical tips

Single Java file can have multiple classes — only one is public, and it must match the filename. Our compiler uses Main as the public class.
Use @Override on methods you mean to override. The compiler will catch typos.
Prefer composition over inheritance when behavior, not identity, is being shared.

Common questions

Can I define multiple classes in one Java file?

Yes. Only the public class must match the filename. Non-public classes can live alongside Main.

What's the difference between abstract class and interface?

Interfaces only declare contracts (and default methods). Abstract classes can hold state and constructors.