How to execute an Array of CompletableFuture and combine their results

Question

I am investigating the use of Java 8 CompletableFuture.

The process I am attempting to code is as follows:-

Extract Keys

1). Execute a single CompletableFuture that returns a List<String>

Extract Data

2). On completion of step 1). Execute multiple CompletableFutures in parallel that accept this List<String>s as input. Each CompletableFuture executed in step 2). returns a unique list of Value Objects.

Combine Data

3). Once all CompletableFutures executed in step 2). have completed I wish to combine the individual lists of Value Objects and complete the process.

The code I have working can only cope with two CompletableFutures executing during Step 2). as follows:-

final CompletableFuture<List<String>> extractor = get("https://example.com//source/url");

final CompletableFuture<List<Documentable>> valueObjectList1 = extractor.thenApplyAsync(s -> callTypeADocumentable(s));
final CompletableFuture<List<Documentable>> valueObjectList2 = extractor.thenApplyAsync(s -> callTypeBCDocumentable(s));

valueObjectList1.thenCombineAsync(valueObjectList2, (c, e) -> consumeBothDocumentable(c, e)).thenAccept(x -> finish(x));

My desired solution is to achieve this:-

final CompletableFuture<List<String>> extractor = get("https://example.com//source/url");

@SuppressWarnings("unchecked")
final CompletableFuture<List<Documentable>>[] completableFutures = new CompletableFuture[ENDPOINT.values().length];

int index = 0;

for (ENDPOINT endpoint : ENDPOINT.values()) {

    final CompletableFuture<List<Documentable>> valueObjectList = extractor.thenApplyAsync(s -> endpoint.contactEndpoit(s));

        completableFutures[index++] = valueObjectList;

    }

completableFutures[0].allOf(completableFutures[1], completableFutures[2], ...);

How can I combine multiple CompletableFutures (e.g. More than two) in the same manner as I did for exactly two CompletableFutures