Additional lessons for the level

equals() and hashCode() contracts or whatever

The equals and hashCode methods are closely related to each other, and it's a good idea to override both methods in a consistent way. Plenty of people know this. But not everyone fully understands the reason for this rule and the consequences for breaking it.

In this post, we'll take a look at the idea behind these methods, review their purpose, and explore why they're so related.

Immutability in Java: final, constants and immutable

In this lesson, we will talk about the special final modifier. You can think of it as a way to "freeze" parts of our program where we need constant, unambiguous, and unchanging behavior.

We can apply it to three elements of our program: classes, methods, and variables. Let's go over them in turn.