What is CompletableFuture in Java?

CompletableFuture (Java 8) is a powerful implementation of Future that supports non-blocking asynchronous programming with a fluent callback API. Unlike plain Future (which only supports blocking get()), CompletableFuture lets you chain operations: thenApply() (transform the result), thenAccept() (consume without returning), thenCompose() (flatMap for futures), thenCombine() (combine two futures). CompletableFuture.supplyAsync(supplier) runs the task in ForkJoinPool. Error handling: exceptionally(), handle(). Combine multiple: allOf() (wait for all), anyOf() (wait for any). This enables readable async pipelines without nested callbacks.