A Visual Diff of Java’s Evolution: Inside java.evolved

Author: A N M Bazlur Rahman

Original post on Foojay: Read More

A community project called java.evolved was recently launched to document how common Java coding patterns have changed across releases. Instead of explaining features in isolation, the site presents “before and after” examples: traditional idioms next to modern alternatives.

The approach targets a practical problem. Most developers work in mixed-era codebases where Java 6, 8, and 17 styles coexist. Rather than memorizing new language features, the site shows what existing code would look like if written today.

Less Boilerplate, More Intent

One example contrasts a classic data class with a record.

Before

public class User {
    private final String name;
    private final int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() { return name; }
    public int getAge() { return age; }
}

After

public record User(String name, int age) {}

The goal is not a new capability but a clearer expression. Modern Java often removes ceremony around concepts that already existed.

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Safer Type Handling and Control Flow

The site also shows improvements in type checks and switch logic.

Pattern matching

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

Switch expression

int letters = switch (day) {
    case MONDAY, FRIDAY, SUNDAY -> 6;
    case TUESDAY -> 7;
    default -> 0;
};

These changes shift common runtime mistakes into compile-time guarantees.

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Why It Matters

Java’s evolution has been gradual, making improvements easy to miss. Seen individually, features look incremental. Seen side by side, they show a significant shift toward readability and correctness.

Community reactions suggest a clear use case: onboarding developers and guiding code reviews in mature systems. Rather than debating style, teams can reference concrete transformations.

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Conclusion

java.evolved acts as a translation layer between past and present Java. By framing language features as recognizable rewrites instead of abstract concepts, it helps developers answer a simple daily question:

“How would we write this today?”

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