The Interpreter Pattern in Light of Java 21
A redux of the classic Gang of Four pattern, "The Interpreter Pattern." This pattern, once relegated as the useless one, has proven more than useless. With the advent of Java 21, it is now a pattern that demands focus in light of sealed classes and pattern matching.
Java 21 is out! Can you believe it? It’s been a long time since I tried Java 1.0 in 1996. It has been amazing how much advancement has happened in Java over the years. Another monumental milestone was the book Design Patterns: Elements of Reusable Object-Oriented Software, also known as the "Gang of Four" book, released in 1994. Both are products of their times, using 1990s languages and tools. It’s now 2023, and we have seen some things. Java now uses lambdas and streams extensively. We now desire immutability. Java’s garbage collection has vastly improved by leaps and bounds. So, while Java has undoubtedly changed, how about our design patterns? That’s why we will discuss one of the patterns from the "Gang of Four" book, the Interpreter Pattern. How do new features like sealed classes, pattern matching, records, and enhanced switch statements in today’s Java change the interpreter pattern? Why is the interpreter so sought out among functional programmers? We will review the classic pattern and its purpose. We replace it with a modern alternative using the latest Java 21 techniques. We discuss its importance and use and how to wire in concepts like programs and monads, thus pushing our knowledge to Java’s edge!