This document provides a detailed explanation of all major features introduced in Java 19 to Java 24, with examples, reasoning for introduction, and previous approaches or limitations.
Issue: Traditional Java threads are heavy, limiting scalability in applications with millions of concurrent tasks.
Introduction: Virtual threads are lightweight, allowing high concurrency with fewer resources.
Example:
Thread.startVirtualThread(() -> System.out.println("Hello from virtual thread"));Issue: Managing multiple threads manually is error-prone and hard to reason about.
Introduction: Structured concurrency treats multiple tasks as a single unit for easier management and error handling.
Example:
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
Future<String> user = scope.fork(() -> fetchUser());
Future<String> orders = scope.fork(() -> fetchOrders());
scope.join();
System.out.println(user.resultNow() + orders.resultNow());
}Issue: Pattern matching for records was limited and verbose.
Example:
record Point(int x, int y) {}
Object obj = new Point(1, 2);
if (obj instanceof Point(int a, int b)) {
System.out.println(a + b); // 3
}Reason: Simplifies interaction with native code and off-heap memory safely.
Example:
MemorySegment segment = MemorySegment.allocateNative(1024);
MemoryAccess.setIntAtOffset(segment, 0, 42);
System.out.println(MemoryAccess.getIntAtOffset(segment, 0));Enhancements for virtual threads, better API and performance.
Issue: Thread-local variables can be cumbersome and error-prone.
Introduction: Scoped values provide a structured way to pass immutable data across threads.
Example:
ScopedValue<String> user = ScopedValue.newInstance();
try (ScopedValue.where(user, "Alice")) {
System.out.println(ScopedValue.get(user)); // Alice
}Issue: Switch statements are verbose and do not handle type patterns.
Example:
Object obj = 42;
switch(obj) {
case Integer i -> System.out.println("Integer: " + i);
case String s -> System.out.println("String: " + s);
default -> System.out.println("Unknown");
}Enhances destructuring capabilities in patterns.
Standardizes lightweight threads for high concurrency.
Improves thread management, making concurrent code easier to write and reason about.
Further improvements to pattern matching with records.
Enhanced switch with type and record patterns.
Issue: Maintaining insertion order in sets and maps was verbose or required LinkedHash* collections.
Example:
SequencedSet<Integer> s = new LinkedHashSet<>();
s.add(3); s.add(1); s.add(2);
System.out.println(s); // [3,1,2]Issue: String concatenation is verbose and error-prone.
Example:
String name = "Alice";
String msg = STR."Hello, \{name}!";
System.out.println(msg); // Hello, Alice!Continued enhancements for pattern matching and destructuring.
Further improvements on switch with patterns.
Enhances structured thread-local data management.
Provides high-performance vector operations for SIMD computation.
Issue: Existing stream collectors lacked composable aggregation methods.
Example:
List<String> list = Stream.of("a","b","c").collect(Collectors.toList());Further improvements to destructuring patterns.
Continued enhancements for type and record matching in switches.
Better structured management of immutable data across threads.
Enhances performance-critical vector operations.
Enhances stream aggregation patterns.
Reason: Simplifies module system import syntax.
Example:
module my.module {
import java.base;
}Reason: Reduces JVM startup time.
Further enhancements for parallel and composable stream operations.
Removes legacy security manager APIs.
Example:
Object obj = 5;
if (obj instanceof Integer i) {
System.out.println(i + 1); // 6
}Enhances expressiveness in constructors.
Improves runtime image creation.
Enhances module import declarations.
Simplifies Java file structure and entry points.
Standard API for cryptography key derivation.
Improves garbage collection with generational ZGC.
Reduces object memory overhead.
Removes legacy GC mode for ZGC.
Improves virtual thread synchronization.
Further enhances runtime image linking.