What Learning Java After PHP Taught Me About OOP

Studying Software Technologies at UniMol after already working with Laravel meant I hit Java's stricter OOP model with real production instincts already formed — and some of them turned out to be wrong.

Interfaces as contracts, enforced by the compiler

PHP lets you be loose about interfaces if you're not disciplined. Java doesn't let you forget:

public interface Repository<T> {
    T findById(Long id);
    List<T> findAll();
}

public class MailboxRepository implements Repository<Mailbox> {
    // compiler error until every method is implemented
}

That enforcement felt restrictive at first and became clarifying once I stopped fighting it — a class that claims to implement an interface genuinely can't lie about it.

Static typing surfaces design problems earlier

A method signature that takes five parameters of the same type is a design smell in any language, but Java's type system makes the smell visible at the call site in a way PHP's looser typing doesn't force you to confront until runtime.

What transferred immediately

Composition over inheritance, single responsibility, dependency injection — these principles didn't need relearning, just a new syntax. The professional experience made the university coursework faster; the coursework made the professional habits more precise about why they work, not just that they do.