docs: use onCompleteFuture() in examples

Author: TomerAberbach

openai-java-example/src/main/java/com/openai/example/CompletionsStreamingAsyncExample.java

@@ -2,10 +2,7 @@
 
 import com.openai.client.OpenAIClientAsync;
 import com.openai.client.okhttp.OpenAIOkHttpClientAsync;
-import com.openai.core.http.AsyncStreamResponse;
 import com.openai.models.*;
-import java.util.Optional;
-import java.util.concurrent.CompletableFuture;
 
 public final class CompletionsStreamingAsyncExample {
     private CompletionsStreamingAsyncExample() {}
@@ -23,23 +20,13 @@ public static void main(String[] args) {
                 .addUserMessage("Tell me a story about building the best SDK!")
                 .build();
 
-        CompletableFuture<Void> onCompleteFuture = new CompletableFuture<>();
-
-        // TODO: Update this example once we support expose an `onCompleteFuture()` method.
-        client.chat().completions().createStreaming(createParams).subscribe(new AsyncStreamResponse.Handler<>() {
-            @Override
-            public void onNext(ChatCompletionChunk completion) {
-                completion.choices().stream()
+        client.chat()
+                .completions()
+                .createStreaming(createParams)
+                .subscribe(completion -> completion.choices().stream()
                         .flatMap(choice -> choice.delta().content().stream())
-                        .forEach(System.out::print);
-            }
-
-            @Override
-            public void onComplete(Optional<Throwable> error) {
-                onCompleteFuture.complete(null);
-            }
-        });
-
-        onCompleteFuture.join();
+                        .forEach(System.out::print))
+                .onCompleteFuture()
+                .join();
     }
 }