add Cf04 demo:二选一任务(applyToEither/acceptEither/runAfterEither)

src/main/java/space/anyi/Cf04_ThenEither.java

@@ -0,0 +1,40 @@
+package space.anyi;
+
+import java.util.concurrent.CompletableFuture;
+
+public class Cf04_ThenEither {
+    public static void main(String[] args) throws Exception {
+        // 场景: 数据优先读本地缓存(快)，缓存没就等远程(慢)，
+        // 谁先返回就用谁，避免干等最慢的那一路
+        CompletableFuture<String> cache = CompletableFuture.supplyAsync(() -> {
+            sleep(100);
+            return "缓存数据";
+        });
+        CompletableFuture<String> remote = CompletableFuture.supplyAsync(() -> {
+            sleep(400);
+            return "远程数据";
+        });
+
+        // applyToEither: 谁先完成用谁的结果，并继续用 BiFunction 加工
+        CompletableFuture<String> result = cache.applyToEither(remote, data -> "优先使用 -> " + data);
+        System.out.println("applyToEither 结果: " + result.join());
+
+        // acceptEither: 谁先完成消费谁的结果，无返回值
+        CompletableFuture<String> a = CompletableFuture.supplyAsync(() -> { sleep(50);  return "A"; });
+        CompletableFuture<String> b = CompletableFuture.supplyAsync(() -> { sleep(400); return "B"; });
+        a.acceptEither(b, s -> System.out.println("acceptEither 选中了先完成的: " + s)).join();
+
+        // runAfterEither: 谁先完成都行，等时间点即可，不关心数据
+        CompletableFuture<Void> r1 = CompletableFuture.runAsync(() -> sleep(60));
+        CompletableFuture<Void> r2 = CompletableFuture.runAsync(() -> sleep(500));
+        r1.runAfterEither(r2, () -> System.out.println("runAfterEither: 有一路先完成了")).join();
+    }
+
+    private static void sleep(long ms) {
+        try {
+            Thread.sleep(ms);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+    }
+}