Skip to content
Ameen Abozaid
Englishالعربية
JNR-001

Modern Java

  • 8 Lessons
  • 87 min of reading
  • 4 h practice (estimate)
Start module
On this page 8 topics

Overview

Topics

  • Release cadence
  • LTS versions
  • records
  • sealed classes
  • switch expressions
  • text blocks
  • pattern matching

Learn first

87 min of reading · 4 h of practice (estimate)

Learning outcomes

  1. Explain Java's six-month release cadence, what LTS means, and how to choose a version for production.
  2. Replace boilerplate data classes with records, including compact constructors that validate.
  3. Model closed hierarchies with sealed interfaces and handle them exhaustively with pattern-matching switch.
  4. Use text blocks, instanceof patterns, and record patterns where they improve readability.

Lessons

  1. 01Java's release model and LTS versions10 min read
  2. 02Records11 min read
  3. 03Sealed classes and interfaces11 min read
  4. 04Switch expressions and pattern matching11 min read
  5. 05Record patterns11 min read
  6. 06Text blocks and other small wins11 min read
  7. 07What changed since the last LTS (updated per release)11 min read
  8. 08Demo: modernizing a legacy Java class step by step11 min read

Lab and exercises

Lab

JNR-001-LAB1 · Shop Core v1

Outcomes: 2–4 · Time: ~2.5 h Model Product, Money, and CartLine as records with validation in compact constructors. Model Discount as a sealed hierarchy (percentage, fixed amount, buy-X-get-Y) and price a cart line with an exhaustive switch. Acceptance: no setters anywhere; adding a new discount type causes a compile error until the switch handles it; no default branch.

Exercises (assessment: refactor a legacy POJO-heavy module and justify each change, plus seven exercises)

IDOutcomeTask
JNR-001-EX011Explain in three sentences the six-month cadence, what LTS means, and which version you would choose for a new production service and why.
JNR-001-EX022Rewrite a Customer class (name, email, getters, setters, equals, hashCode, toString) as a record. Reject a blank name.
JNR-001-EX032A record has a List<String> tags component. Show how a caller can break it and fix it.
JNR-001-EX043Declare a sealed interface PaymentMethod with Card, Cash, Voucher. Write a switch returning a fee for each.
JNR-001-EX053Add Transfer to PaymentMethod without touching the switch. What happens? Why is default harmful here?
JNR-001-EX064Rewrite a chain of if (o instanceof X) { X x = (X) o; ... } with pattern matching, and a concatenated JSON string with a text block.
JNR-001-EX074Use a record pattern to print Money(cents, currency) from an Object using instanceof.
Show solutions
  • EX01 Releases every six months (March, September); LTS gets years of support; pick the current LTS, because it is patched for a long time (verify the version).
  • EX02 record Customer(String name, String email) { Customer { if (name == null || name.isBlank()) throw new IllegalArgumentException("name"); } }.
  • EX03 The caller keeps the original list and changes it. Fix: tags = List.copyOf(tags); in the compact constructor.
  • EX04 sealed interface PaymentMethod permits Card, Cash, Voucher {} (records); switch (m) { case Card c -> ...; case Cash c -> ...; case Voucher v -> ...; }.
  • EX05 The code fails to compile: the switch is not exhaustive. With default, it would compile and silently use the wrong fee.
  • EX06 if (o instanceof Product p) { ... p.name() ... }; a text block with three quotes and no escaped quotes.
  • EX07 if (o instanceof Money(long cents, String currency)) { System.out.println(cents + " " + currency); }.
  • Outcome 1 is also covered by quiz Q01–Q03; the lab covers outcomes 2–4.

Quiz

Outcomes: O1 release model and LTS · O2 records · O3 sealed types and switch · O4 patterns, text blocks.

A self-check for you: nothing is graded, saved or sent anywhere. Choose an answer, then check it. You can try again as often as you like.

  1. 1How often does a new Java version appear?O1
  2. 2What does LTS mean?O1
  3. 3Preview features in production code are:O1
  4. 4A record automatically gives you:O2
  5. 5Where do you validate record values?O2
  6. 6A record has a List component. To keep it safe you:O2
  7. 7What does sealed ... permits do?O3
  8. 8A switch over a sealed type with a missing case:O3
  9. 9Why avoid default in that switch?O3
  10. 10if (o instanceof String s) does:O4

Practical part

Seven exercises JNR-001-EX01 to EX07, the legacy-refactoring task, and the lab. Pass: at least 8 of 10 quiz answers, six exercises correct, and a lab that fails to compile when a discount type is unhandled.

Common mistakes

Records with mutable components (lists not copied); default branches that defeat exhaustiveness; using preview features in production code.

Assessment

Refactor a legacy POJO-heavy module to modern Java and justify each change.

Career relevance

Modern codebases and interviews expect these features; sealed types reappear in event modeling (SRB-002).

Type to search levels, phases, modules and lessons.