concurrency4CompletableFutureDemo

1package pkg7concurrency;2 3/*4 * concurrency4CompletableFutureDemo.java5 * --------------------------6 * Asynchronous pipelines: chain, combine, and handle errors without blocking.7 *8 * KEY METHODS:9 *   supplyAsync / runAsync   : start async work.10 *   thenApply / thenCompose  : transform / flat-map the result.11 *   thenCombine              : combine two independent futures.12 *   exceptionally / handle   : recover from failures.13 *   allOf / anyOf            : coordinate multiple futures.14 */15import java.util.concurrent.*;16 17public class concurrency4CompletableFutureDemo {18 19    static int slow(int x) {20        try { Thread.sleep(30); } catch (InterruptedException ignored) {}21        return x;22    }23 24    public static void main(String[] args) throws Exception {25        // Chain transformations26        CompletableFuture<String> pipeline = CompletableFuture27                .supplyAsync(() -> slow(10))28                .thenApply(x -> x * 2)               // 2029                .thenApply(x -> "result=" + x);30        System.out.println(pipeline.get());31 32        // thenCompose: dependent async step (flat-map)33        CompletableFuture<Integer> composed = CompletableFuture34                .supplyAsync(() -> slow(5))35                .thenCompose(x -> CompletableFuture.supplyAsync(() -> x + 100));36        System.out.println("composed: " + composed.get());37 38        // thenCombine: merge two independent computations39        CompletableFuture<Integer> a = CompletableFuture.supplyAsync(() -> slow(3));40        CompletableFuture<Integer> b = CompletableFuture.supplyAsync(() -> slow(4));41        System.out.println("combined a+b: " + a.thenCombine(b, Integer::sum).get());42 43        // Error handling44        CompletableFuture<Integer> recovered = CompletableFuture45                .<Integer>supplyAsync(() -> { throw new RuntimeException("boom"); })46                .exceptionally(ex -> { System.out.println("recovered from: " + ex.getMessage()); return -1; });47        System.out.println("recovered value: " + recovered.get());48 49        // allOf: wait for many50        CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(() -> slow(1));51        CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(() -> slow(2));52        CompletableFuture.allOf(f1, f2).join();53        System.out.println("allOf done: " + f1.get() + ", " + f2.get());54    }55}