Lessons

In this lecture we cover closed hierarchies in Java 17+: how to declare classes and interfaces with the sealed modifier, specify allowed subclasses via permits, choose the status of subclasses ( final, sealed, non-sealed), and why this strengthens exhaustiveness checking of switch with pattern matching without a default branch. We’ll look at examples with domain models, interaction with interface and record, as well as typical mistakes.

Let’s break down how, starting with Java 16+, type checking became simpler thanks to pattern matching for instanceof: you check the type and immediately declare a variable of the required type ( if (obj instanceof String s) {...}). We’ll compare it with the “old” approach using explicit casting ( ( String )), discuss variable scope, working with null, inheritance, limitations, and common mistakes. Less boilerplate — better readability and safety (without ClassCastException).

In this lecture, we break down the modern switch with pattern matching: case branches with automatic type narrowing, handling null via case null, guard conditions when, exhaustive checks with sealed hierarchies, and nested patterns for record. We show practical examples, nuances, JDK 21+ requirements, and common mistakes.

We break down pattern matching for record classes in Java 21+: how to destructure components right in instanceof and switch, use nested patterns and when guard expressions, and build expressive and safe code on top of record classes and sealed hierarchies. Practical examples, limitations, a comparison table, and common mistakes.

A quick guide to the pitfalls of modern language features: the scope of pattern variables in instanceof, behavior with null (including switch branches), nuances of sealed/ permits hierarchies and the requirement for default, limitations of record-patterns, as well as compatibility with JDK and IDE versions. To wrap up — a motivational congratulations on completing the Java 25 course.

The final project of the course: apply all the knowledge gained about SQL and PostgreSQL to solve a comprehensive task. In this project you'll solidify skills working with tables, queries, indexes, transactions, and optimization.

This section presents the course final project: the capstone assignment where you can apply all the knowledge you've gained about SQL and PostgreSQL in practice. Test your skills with queries, aggregates, subqueries, indexes, and optimization!

The final stage of the course: the final project on SQL and PostgreSQL. Here you can apply all the knowledge you've gained in practice, implement your own database, write complex queries, and demonstrate skills in optimization and data analysis.

Capstone project of the course: here you can apply all the knowledge you've gained about SQL and PostgreSQL in practice by solving a comprehensive task that mirrors real-world database work.

This section presents the course final project: the capstone assignment where you can apply all the knowledge you've gained about SQL and PostgreSQL in practice. Test your skills with queries, aggregates, subqueries, indexes, and optimization!