Java 20 to Java 24: A Comprehensive Guide for Freshers

Java has evolved significantly from version 20 to 24, introducing features that improve developer productivity, enhance performance, and modernize the language. This article explores the key features of each version, supported by examples and graphical representations to help freshers understand these advancements. We’ll also compare their performance and usability.

Java 20 Features

Released in March 2023, Java 20 introduced several enhancements focused on simplifying coding practices and improving runtime performance.

Key Features

1. Pattern Matching for instanceof: Simplifies type checks by eliminating explicit casting.

if (obj instanceof String str) {
    System.out.println(str.toUpperCase());
}        

2. Sealed Classes: Restricts which classes can extend a parent class.

public sealed class Shape permits Circle, Rectangle {}        

3. Improved Switch Statements: Supports multiple case labels in a single branch.

switch (day) {
    case MONDAY, FRIDAY -> System.out.println("Busy day!");
    default -> System.out.println("Relaxing day!");
}        

4. Records: Simplifies immutable data classes.

record Point(int x, int y) {}        

Java 21 Features (LTS)

Released in September 2023, Java 21 is a Long-Term Support (LTS) version that finalized several preview features.

Key Features

1. Virtual Threads: Lightweight threads for scalable concurrency.

Thread.startVirtualThread(() -> System.out.println("Hello from virtual thread!"));        

2. Sequenced Collections: Provides ordered access to collection elements.

SequencedSet<String> set = new SequencedSet<>();
set.add("A");
System.out.println(set.first()); // A        

3. Record Patterns: Enables pattern matching with records.

if (obj instanceof Point(int x, int y)) {
    System.out.println("x: " + x + ", y: " + y);
}        

4. String Templates (Preview): Simplifies string interpolation.

String name = "Alice";
System.out.println(`Hello, ${name}!`);        

Java 22 Features

Released in March 2024, Java 22 introduced streamlined coding practices and enhanced APIs.

Key Features

1. Unnamed Variables & Patterns: Allows placeholders for unused variables.

if (obj instanceof Point(var x, _)) {
    System.out.println("x: " + x);
}        

2. Stream Gatherers: Custom intermediate operations in streams.

List<Integer> squares = Stream.of(1, 2, 3)
    .collect(StreamGatherer.gatheringToList(x -> x * x));        

3. Statements Before super(): Allows initialization before calling the parent constructor.

class Child extends Parent {
    Child() {
        int value = computeValue();
        super(value);
    }
}        

Java 23 Features

Released in September 2024, Java 23 focused on modularity and concurrency improvements.

Key Features

1. Scoped Values: Efficiently share immutable data across threads.
2. Structured Concurrency: Manage multiple tasks as a single unit.

try (var scope = StructuredTaskScope.open()) {
    Future<String> task1 = scope.fork(() -> fetchData());
    scope.join();
}        

3. Module Import Declarations: Simplify module imports directly in source files.

Java 24 Features

Released in March 2025, Java 24 introduces performance enhancements and quantum-safe encryption.

Key Features

1. Quantum-Safe Encryption: Future-proof cryptographic algorithms.
2. Compact Object Headers: Reduces memory usage by optimizing object headers.
3. Ahead-of-Time Class Loading: Improves application startup time.

Graphical Comparison of Java Versions

Feature Comparison

Performance Comparison

The graph below compares runtime memory usage and execution speed across versions:

• Java 24 shows the best performance due to compact object headers and ahead-of-time loading.

Conclusion

Each version of Java from 20 to 24 brings unique enhancements that cater to modern development needs:

• For beginners, starting with Java 21 (LTS) is recommended due to its stability and finalized features like virtual threads and record patterns.
• Advanced developers can leverage cutting-edge features in Java 24 for improved performance and security.

By understanding these advancements and their practical applications, developers can write cleaner, faster, and more secure code while staying ahead in the rapidly evolving world of software development.