Guided: Apply Records and Pattern Matching in Java Services

Table of Contents

1. Challenge

   Introduction

   Welcome to this Code Lab on modern Java features! You'll explore how records and pattern matching can significantly reduce boilerplate and improve the clarity and safety of your code. You'll start with a traditional Java application and refactor it step by step.

   Before you dive into writing new code, familiarize yourself with the project structure. You're working with a standard Maven project where the main logic lives in src/main/java and tests are in src/test/java. Explore the files, especially LegacyBook.java, which you'll refactor first, and MediaService.java, where you'll implement pattern matching.

   Navigation Tip: For easier code navigation, collapse the Workspace view in the Explorer pane and expand the Projects view instead. The Projects view organizes your Java files by package structure, making it much simpler to locate classes and interfaces.

   You'll see two main projects:

   • LAB-CODE: Your working code that you'll modify throughout the exercises
   • SOLUTION: Reference implementations for each step (files follow the pattern FILENAME-STEP#-TASK#.java, e.g., Book-2-1.java)

   Start by expanding LAB-CODE to see the source code you'll be working with. If you get stuck on any task, you can reference the corresponding solution file for guidance.

   info> This lab experience was developed by the Pluralsight team using Forge, an internally developed AI tool utilizing Gemini technology. All sections were verified by human experts for accuracy prior to publication. For issue reporting, please contact us.

2. Challenge

   Step 2: From Verbose Classes to Concise Records

   A common task in Java is creating classes to simply hold data, like results from a database query or a network request. Historically, this meant writing a lot of boilerplate: private final fields, a constructor, accessor methods, and equals(), hashCode(), and toString() implementations. These classes are often called Plain Old Java Objects (POJOs) or data transfer objects (DTOs).

   Java records, introduced as a standard feature in Java 16, are designed to eliminate this ceremony. They are a special, more restricted kind of class, optimized for the role of being a simple, immutable data aggregate.

3. Challenge

   Step 3: Building a Data Model with Records

   Now that you understand the basics of records, build out your data model. By using records for all your data-carrying objects, you ensure they are simple, immutable, and consistent. This also sets you up perfectly for using pattern matching in the next steps.

   You'll also use a sealed interface named Media. A sealed interface restricts which other classes or interfaces may extend or implement it. This gives the compiler a complete picture of the type hierarchy, which is essential for exhaustive checks in pattern matching.

4. Challenge

   Step 4: Simplifying `instanceof` Checks

   A very common code pattern in Java is checking if an object is an instance of a specific type, and if so, casting it to that type to call one of its methods. This pattern is verbose and contains a redundancy: the type is mentioned twice.

   if (obj instanceof String) {
       String s = (String) obj;
       System.out.println(s.length());
   }
   

   Pattern matching for instanceof (a standard feature since Java 16) streamlines this. It lets you declare a new variable of the target type, which is only in scope if the check succeeds. This makes the code more concise and removes the need for the manual cast.

5. Challenge

   Step 5: Advanced Data Handling with `switch` Expressions

   The final feature you'll explore is pattern matching for switch expressions, made standard in Java 21. This feature elevates switch from a simple control flow statement to a powerful tool for data-oriented programming. You can switch on an object and have case labels that match against types, not just constant values.

   When you use this with records and sealed interfaces, it allows for exhaustive and elegant handling of different data types. The compiler can verify that you've handled all permitted subtypes of a sealed interface, eliminating a whole class of runtime errors. -----

   Congratulations on completing the lab! You've successfully modernized a Java application using records and pattern matching.

   You've learned how to:

   • Replace verbose POJOs with concise record types for immutable data.
   • Simplify instanceof checks and casts using pattern matching.
   • Rewrite cumbersome if-else chains as elegant and type-safe switch expressions.

   These modern Java features help you write code that is not only shorter but also more readable, robust, and a pleasure to maintain.