Guided: Type Inference and Intro to Pattern Matching

Table of Contents

1. Challenge

   Introduction

   Welcome to this Code Lab on modernizing Java! You'll take an existing application written with older Java syntax and refactor it using two powerful features: Local-Variable Type Inference (var) and Pattern Matching for instanceof. These features help make your code less verbose, more readable, and less prone to common errors like casting mistakes.

   You have a simple media library application. It has a MediaProcessor that processes a list of Media objects, which can be either a Book or a Movie. Look at the files, especially MediaProcessor.java. Notice the classic instanceof checks followed by explicit casts. Your goal is to clean this up.

   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: Refactoring with the 'var' Keyword

   Use the var keyword to let the Java compiler infer the type of a local variable from its initializer. This is purely a compile-time feature that can significantly reduce boilerplate code, especially when dealing with long, complex type names like nested generics.

3. Challenge

   Step 3: Simplifying Logic with 'instanceof' Pattern Matching

   Pattern matching for instanceof streamlines a common coding pattern: checking if an object is of a certain type, and if so, casting it and using it. Use the new syntax to test, bind the result to a new variable of the correct type, and use it, all in one go. The new pattern variable is only in scope where it's guaranteed to have been assigned, making your code safer.

4. Challenge

   Step 4: Applying Pattern Matching in Domain Models

   The equals() method is a perfect candidate for refactoring with pattern matching. The old way requires several lines of boilerplate to safely check the type and cast. Simplify it to a single, expressive line.

5. Challenge

   Step 5: Conclusion

   Congratulations on completing the Code Lab! You've successfully used var and instanceof pattern matching to modernize a Java application. Compare the final code to what you started with. It's cleaner, more concise, and easier to understand. Apply these powerful features to your own Java projects.