The java.util.concurrent.CompletableFuture<T> class was first introduced in Java 8. It is the next level of asynchronous call control over java.util.concurrent.Future<T> interface. It actually implements Future, as well as java.util.concurrent.CompletionStage<T>. In Java 9, CompletableFuture was enhanced by adding new factory methods, support for delays and timeouts, and improved subclassing--we will discuss these features in more details in the sections to follow. But first, let's have an overview of the CompletableFuture API.
The CompletableFuture API consists of more than 70 methods, 38 of which are implementations of the CompletionStage interface, and five are the implementations of Future. Because the CompletableFutureclass implements the Future interface, it can be treated as Future and will not break the existing functionality based on the Future API.
So, the bulk of the API comes...