completablefuture-chaining.yaml

---
id: 50
slug: "completablefuture-chaining"
title: "CompletableFuture chaining"
category: "concurrency"
difficulty: "intermediate"
jdkVersion: "8"
oldLabel: "Pre-Java 8"
modernLabel: "Java 8+"
oldApproach: "Blocking Future.get()"
modernApproach: "CompletableFuture"
oldCode: |-
  Future<String> future =
      executor.submit(this::fetchData);
  String data = future.get(); // blocks
  String result = transform(data);
modernCode: |-
  CompletableFuture.supplyAsync(
      this::fetchData
  )
  .thenApply(this::transform)
  .thenAccept(IO::println);
summary: "Chain async operations without blocking, using CompletableFuture."
explanation: "CompletableFuture enables non-blocking async pipelines. Chain operations\
  \ with thenApply, thenCompose, thenAccept. Handle errors with exceptionally(). Combine\
  \ multiple futures with allOf/anyOf."
whyModernWins:
- icon: "🔗"
  title: "Chainable"
  desc: "Compose async steps into a readable pipeline."
- icon: "🚫"
  title: "Non-blocking"
  desc: "No thread sits idle waiting for results."
- icon: "🛡️"
  title: "Error handling"
  desc: "exceptionally() and handle() for clean error recovery."
support:
  state: "available"
  description: "Widely available since JDK 8 (March 2014)"
prev: "concurrency/stable-values"
next: "concurrency/executor-try-with-resources"
related:
- "concurrency/stable-values"
- "concurrency/scoped-values"
- "concurrency/structured-concurrency"
docs:
- title: "CompletableFuture"
  href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/concurrent/CompletableFuture.html"