JEP 526 Simplifies Deferred Initialization Ahead of JDK 26

JEP 526 Simplifies Deferred Initialization Ahead of JDK 26

JEP 526, now in second preview, replaces the earlier Stable Values API with Lazy Constants for JDK 26. This update enables immutable, thread-safe deferred initialization of computed constants, eliminating manual synchronization patterns like double-checked locking.

Why This Matters

Traditional lazy-initialization techniques—such as double-checked locking or holder classes—require careful thread-safety handling and often introduce boilerplate code. Lazy Constants abstract this complexity, allowing the JVM to optimize cached values as true constants post-initialization. For large systems, this reduces startup overhead by deferring initialization of unused resources like loggers or caches, while ensuring immutability and eliminating null ambiguity.

Key Insights

• “JEP 526 renamed from Stable Values in 2025 to emphasize laziness and immutability”: https://www.infoq.com/news/2025/12/jep526-lazy-constants/
• “LazyConstant disallows null to prevent ambiguity and align with unmodifiable constructs”
• “Lazy lists and maps enable on-demand resource pooling, reducing upfront memory allocation”

Working Example

private static final LazyConstant<Logger> LOG =
    LazyConstant.of(() -> Logger.create(MyService.class));

void run() {
    LOG.get().info("service started");
}

static final List<OrderController> ORDERS =
    List.ofLazy(POOL_SIZE, _ -> new OrderController());

OrderController controller() {
    long index = Thread.currentThread().threadId() % POOL_SIZE;
    return ORDERS.get((int) index);
}

static final Map<String, OrderController> ORDERS =
    Map.ofLazy(Set.of("Customers", "Internal", "Testing"),
               _ -> new OrderController());

OrderController controller() {
    return ORDERS.get(Thread.currentThread().getName());
}

Practical Applications

• Use Case: Java frameworks using LazyConstants for on-demand resource pools (e.g., controller instances)
• Pitfall: Overusing LazyConstants for trivial initializations, which may introduce unnecessary complexity

References:

• https://www.infoq.com/news/2025/12/jep526-lazy-constants/

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