Java Since Java 8: What Has Changed? A Guide for Getting Back In

This article summarizes the most important changes in the Java ecosystem from Java 8 to Java 21 for developers returning after a break.

Top 10 Changes Since Java 8¶

1. Records (Java 16) — Immutable data classes in a single line, with automatic constructors, equals(), hashCode(), and toString()
2. var (Java 10) — Local type inference; the compiler infers types at compile time (not dynamic like JavaScript)
3. Text Blocks (Java 15) — Multi-line strings with """...""", no more string concatenation or \n
4. Pattern Matching (Java 16/21) — instanceof without explicit cast; switch with type patterns and guards
5. Sealed Classes (Java 17) — Restrict which classes can extend an interface/class; compiler knows all possible subtypes
6. Switch Expressions (Java 14) — switch now returns a value; arrow syntax (->) and yield
7. Virtual Threads (Java 21) — Millions of lightweight threads with minimal overhead; Spring Boot 3.2+ supports them with one config line
8. Module System (Java 9) — Project Jigsaw; most applications still use the classpath but modules exist
9. New Collection Methods — List.of(), Set.of(), Map.of(), .toList(), getFirst()/getLast()
10. Built-in HTTP Client (Java 11) — java.net.http.HttpClient replaces the old HttpURLConnection

Key Code Comparison¶

// Java 8 style: 38-line class
class Benutzer {
    private String vorname;
    private String nachname;
    private int alter;
    // constructor, getters, equals, hashCode, toString...
}

// Java 21 style: 1 line
record Benutzer(String vorname, String nachname, int alter) {}

JDK Distribution Landscape¶

Oracle is no longer the only JDK provider. The recommended distribution is Eclipse Temurin (by the Eclipse Foundation / Adoptium) — free, TCK-tested, and backed by IBM, Red Hat, and Microsoft. Install and manage multiple Java versions with SDKMAN:

curl -s "https://get.sdkman.io" | bash
sdk install java 21.0.4-tem

Virtual Threads (Java 21)¶

Virtual threads are the biggest change since lambdas. Where traditional OS threads cost ~1 MB of stack each, virtual threads are cheap enough to spawn millions:

// Spring Boot 3.2+: one line in application.properties
// spring.threads.virtual.enabled=true

// Or manually:
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 1_000_000; i++) {
        executor.submit(() -> { /* I/O work */ });
    }
}

Ecosystem Quick Reference¶

Recommended Stack for New Projects¶

• JDK: Eclipse Temurin 21
• Build: Maven or Gradle
• Framework: Spring Boot 3.x
• IDE: IntelliJ IDEA Community Edition
• Testing: JUnit 5