28 posts tagged with "Java"

If fields are private but setters are public, isn't that the same as making the field public? And what's the difference between Long and long anyway? Let's clear up these common Java confusions.

"What do .stream(), .map(), and .collect() actually do?" These three methods form a powerful pipeline for transforming collections in Java. Instead of writing loops to transform each element, you create a stream, transform elements, and collect results. Let's break down exactly what happens at each step.

"Why do we need both generateToken() (public) and createToken() (private) instead of just one method?" Because separation of concerns makes your code extensible. The public method handles what claims to add (business logic), while the private method handles how to build the JWT (technical details). This lets you add new token types without repeating code. Let's understand why this design pattern is essential.

"What does ResponseEntity<UnlockResponse> mean? Why can I use <UnlockResponse> here but <LoginResponse> somewhere else?" ResponseEntity is like a delivery box - it's a generic container that can hold any type of content. The <T> is a placeholder that you fill with your specific data type. Let's understand how this "magic" works and why it's incredibly powerful.

In Part 1, we learned why Spring Data JPA repositories must be interfaces. Now let's understand the fundamental difference between classes and interfaces in Java, and when to use each.

In Parts 1 and 2, we learned what interfaces are and when to use them. Now let's dive deep into the OOP principles that make interfaces essential for large-scale applications. This isn't about avoiding code duplication—it's about fundamental software design.

"Why can't I use class instead of interface for UserRepository?" Because Java's type system has strict rules: class extends class, interface extends interface, class implements interface. When you try class UserRepository extends JpaRepository, Java sees JpaRepository is an interface and throws an error. Let's understand the three-level inheritance chain and who implements what.

Trying to create a Spring Data repository by extending JpaRepository with a class instead of an interface? It won't work. Here's why Spring Data JPA requires interfaces and what happens behind the scenes.

"Can't we just create a utility class with static methods instead of using interfaces? Isn't the interface approach just fancy?" Great question! Yes, you could use utility classes - but you'd be solving only 50% of the problem. Let's see what happens in practice and why interfaces aren't fancy, they're necessary.

How do you prevent typos like "admin", "Admin", "ADMIM" when storing user roles? Use Java enums! Here's how to add type-safe roles to your JPA entities.