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Concurrency intermediate

CompletableFuture chaining

Chain async operations without blocking, using CompletableFuture.

Code Comparison
✕ Pre-Java 8 
Future<String> future =
    executor.submit(this::fetchData);
String data = future.get(); // blocks
String result = transform(data);
✓ Java 8+ 
CompletableFuture.supplyAsync(
    this::fetchData
)
.thenApply(this::transform)
.thenAccept(System.out::println);
Why the modern way wins
🔗

Chainable

Compose async steps into a readable pipeline.

🚫

Non-blocking

No thread sits idle waiting for results.

🛡️

Error handling

exceptionally() and handle() for clean error recovery.

Old Approach
Blocking Future.get()
Modern Approach
CompletableFuture
Since JDK
8
Difficulty
intermediate
JDK Support
CompletableFuture chaining
Available

Widely available since JDK 8 (March 2014)

How it works

CompletableFuture enables non-blocking async pipelines. Chain operations with thenApply, thenCompose, thenAccept. Handle errors with exceptionally(). Combine multiple futures with allOf/anyOf.

Related patterns

Concurrency advanced

Stable values

Java 8
private volatile Logger logger;
Logger getLogger() {
    if (logger == null) {
        synchronized (this) {
            if (logger == null)
                logger = createLogger();
        }
    }
    return logger;
}
Java 25
private final StableValue<Logger> logger =
    StableValue.of(this::createLogger);

Logger getLogger() {
    return logger.get();
}
Hover to see modern ➜
JDK 25+ →
Concurrency advanced

Scoped values

Java 8
static final ThreadLocal<User> CURRENT =
    new ThreadLocal<>();
void handle(Request req) {
    CURRENT.set(authenticate(req));
    try { process(); }
    finally { CURRENT.remove(); }
}
Java 25
static final ScopedValue<User> CURRENT =
    ScopedValue.newInstance();
void handle(Request req) {
    ScopedValue.where(CURRENT,
        authenticate(req)
    ).run(this::process);
}
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JDK 25+ →
Concurrency advanced

Structured concurrency

Java 8
ExecutorService exec =
    Executors.newFixedThreadPool(2);
Future<User> u = exec.submit(this::fetchUser);
Future<Order> o = exec.submit(this::fetchOrder);
try {
    return combine(u.get(), o.get());
} finally { exec.shutdown(); }
Java 25
try (var scope = new StructuredTaskScope
        .ShutdownOnFailure()) {
    var u = scope.fork(this::fetchUser);
    var o = scope.fork(this::fetchOrder);
    scope.join().throwIfFailed();
    return combine(u.get(), o.get());
}
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JDK 25+ →
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