May 15, 20241 min de lecturacode

A Guide to Pattern Matching and Sealed Classes in Java 21

Writing Safer and More Expressive Java Code

Java 21 introduces powerful enhancements that improve readability, safety, and expressiveness in your code. Among these, pattern matching and sealed classes stand out, allowing developers to write concise, readable, and safe code. Let's explore both concepts with practical examples.

Pattern Matching for Switch

Pattern matching extends the classic switch statement, making code simpler and clearer by reducing the need for explicit casting and type checking.

Traditional Switch

Object obj = "Hello";

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

Pattern Matching Switch

Object obj = "Hello";

switch (obj) {
    case String s -> System.out.println(s.toLowerCase());
    case Integer i -> System.out.println(i + 1);
    default -> System.out.println("Unknown type");
}

Benefits:

Reduced boilerplate code
Enhanced readability
Improved type safety

Sealed Classes

Sealed classes allow you to define which subclasses or implementations are permitted. This helps in modeling clear and controlled domain hierarchies.

Declaring a Sealed Class

public sealed abstract class Shape
    permits Circle, Rectangle {}

public final class Circle extends Shape {
    double radius;
}

public final class Rectangle extends Shape {
    double length, width;
}

Using Pattern Matching with Sealed Classes

Shape shape = new Circle();

double area = switch (shape) {
    case Circle c -> Math.PI * c.radius * c.radius;
    case Rectangle r -> r.length * r.width;
};

System.out.println("Area: " + area);

Benefits:

Enhanced clarity of inheritance hierarchies
Compile-time enforcement of permitted subclasses
Simplified, safer code when used with pattern matching

Practical Applications

Domain modeling with restricted class hierarchies
Type-safe parsing and processing of structured data
Cleaner implementations of polymorphic behavior

Pattern matching and sealed classes provide significant improvements in Java 21, helping you write cleaner, safer, and more maintainable code. Mastering these tools allows developers to leverage the full expressive power of modern Java.