CompletableFuture composes asynchronous work

thenCombine joins two independent results, and join waits without a checked exception - the readable way to run calls in parallel and merge them.

Code

CompletableFuture<Integer> price = CompletableFuture.supplyAsync(() -> {
    try { Thread.sleep(20); } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
    return 100;
});
CompletableFuture<Integer> tax = CompletableFuture.supplyAsync(() -> 18);

CompletableFuture<String> total = price.thenCombine(tax, (p, t) -> "total = " + (p + t));
System.out.println(total.join());

var chained = CompletableFuture.supplyAsync(() -> "jch")
        .thenApply(String::toUpperCase)
        .thenApply(s -> s + " ready");
System.out.println(chained.join());

Output

total = 118
JCH ready

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Published 2026-07-30