尝试更新ComppletableFuture变量但收到错误：从lambda表达式引用的局部变量必须是最终的或有效的最终变量

Question

public CompletableFuture<String> description() {
    CompletableFuture<String> result = CompletableFuture
            .supplyAsync(() -> "Search for: " + this.stop + " <-> " + name + ":\n")
            .thenApply(x -> x += "From " +  this.stop + "\n");

    CompletableFuture<Void> temp = services.thenAccept(x -> {
      for (BusService service : x.keySet()) {
        CompletableFuture<Set<BusStop>> stops = x.get(service);
        result = result.thenApply(y -> y += describeService(service, stops));
      }
    });
    return result;
  }

  
  public CompletableFuture<String> describeService(BusService service,
                                                   CompletableFuture<Set<BusStop>> stops) {

    return stops.thenApply(x -> {
      if (x.isEmpty()) {
        return "";
      }
      return x.stream()
              .filter(stop -> stop != this.stop)
              .reduce("- Can take " + service + " to:\n",
                      (str, stop) -> str += "  - " + stop + "\n",
                      (str1, str2) -> str1 + str2);
    });

  }

我试图在deatsture（）中的forloop中更新结果，因为result.thenApply（）导致一个新的ComppletableFuture实例，我需要将其重新分配给一个新变量以更新结果，但我不太确定如何

Answer 1

您不需要将其重新分配给新变量，也不应该这样做。而是合并期货。

return services.thenCombine(result, (x, y) -> {
  for (BusService service : x.keySet()) {
    CompletableFuture<Set<BusStop>> stops = x.get(service);
    y += describeService(service, stops);
  }
  return y;
});