Java 17 Sealed Classes Explained | Crack Your Java Interview

Publié le: 02 mai 2026
sur la chaîne: The Curious Coder

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Sealed Classes in Java 17 are one of the most asked topics in Java interviews — and most devs answer it wrong. In this video, I break it down completely, from WHY they exist to HOW to implement them with hands-on coding.

If you've ever tried to control inheritance in Java using just the ‘final’ keyword, you already know its limitations. And if you've tried to work around it using multiple packages — you've probably hit a wall there too.

That's exactly the problem Java 17 set out to solve with Sealed Classes — and understanding why they were introduced is what separates a good answer from a great one in a Java interview.

In this video, we start from scratch. No assumptions. We first revisit how inheritance works in Java, where traditional approaches break down, and then build up to Sealed Classes step by step — so by the time we touch the code, you actually understand what you're writing and why.

We then move into hands-on coding in IntelliJ IDEA, where you'll see exactly how to declare a Sealed Class, how to use the ‘permits’ keyword to give specific classes the right to inherit it, and what happens when you violate the contract Java enforces.

And yes — there are rules. Sealed Classes come with strict compile-time constraints that Java enforces on both the sealed class and its permitted subclasses. These rules are frequently tested in interviews, and knowing not just what they are but why they exist will help you explain them confidently under pressure.

By the end of this video, you'll be able to:

✅ Explain what a Sealed Class is and the exact problem it solves
✅ Walk through the evolution of inheritance control in Java — from ‘final’ to packages to sealed
✅ Write Sealed Classes from scratch with proper ’permits’ declarations
✅ Understand what Java strictly enforces on subclasses of a sealed class — and why
✅ Understand sealed vs non-sealed vs final

Whether you're preparing for interviews at a product-based company or just want to deeply understand Java 17's new features, this one's worth your full attention.

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00:00 : Why were Sealed Classes introduced in Java 17
00:54 : Problem with final Keyword — and Its Limitations
02:39 : package-private vs sealed
05:42 : sealed class Hands-On
07:40 : sealed vs non-sealed vs final
12:08 : Sealed Classes Rule: Permitted Classes MUST extend it
12:55 : Sealed Class Rule: Subclasses must be in same Package

#Java17 #SealedClasses #JavaInterviewQuestions #Java17Features #JavaProgramming
#BackendDevelopment #SpringBoot #JavaDeveloper #CodingInterviewPrep #JavaTutorial

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