This article presents an implementation of a Hospital Management System using Java 21. If we say using Java 21, it means we are free to use all the final features that are available till Java 21. It doesn't matter whether a particular feature belongs to Java 8 or Java 21. The used feature should be available till Java 21. Our focus would be on some progressive features such as sealed classes, records, pattern matching in switch, immutable collections, and formatted string output. Along the way, we’ll also explore how these features simplify code design, improve safety, and enhance readability. The primary target of this article is to practice the most important & latest features of Java in a real world use