A little bit of Java17

• Sealed Classes

Sealed Classes were introduced in Java 17 as part of improvements related to object-oriented programming, allowing greater restrictions on class inheritance. This functionality gives you more control over which classes can extend or implement a class or interface, helping to keep your code safer.

Let's create a step-by-step tutorial on how to use Sealed Classes in Java 17.

First, let's create a class called Bank and add the “sealed” modifier to it, which controls how other classes or interfaces can extend or implement the class or interface.

Doing this, we can see that we have an error indicating that the Bank class with “sealed” modifier needs to have subclasses.

To solve this problem, we will create a class called Customer and add the “permits” clause to the Bank class.

By doing this we can see that we have the following error.

> Invalid permits clause: ‘Cliente’ must directly extend ‘Bank’

That's exactly what you're thinking, to solve this problem we need to extend the Bank class directly into the Customer class.

This solves our problem and with that we can now use our Sealed Class, cool isn’t it?

> NOTE: The concept of sealed can also be applied to interfaces in Java 17. Just like classes, a sealed interface can restrict which other interfaces or classes can implement it.

Conclusion:
Sealed Classes offer a powerful way to restrict and control inheritance in Java. With this, you can prevent classes from being extended by mistake, improving code readability and security.

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