CompletableFutures and applyAsync in Java

CompletableFutures are a useful tool in Java for building asynchronous and concurrent programs. They provide a way to model computations that can be executed asynchronously and provide a callback mechanism for handling the results.

One method of creating a CompletableFuture is through applyAsync. This method is used to create a CompletableFuture that will be executed asynchronously and will return a value.

public static <U> CompletableFuture<U> applyAsync(Supplier<U> supplier)

The applyAsync method takes in a supplier function that returns the result of the computation. This supplier function will be executed asynchronously and the CompletableFuture returned from applyAsync will complete with the result of the supplier function when it is done.

Here is an example of using applyAsync to create a CompletableFuture that returns a string:

CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
    // Compute result
    return "Hello, CompletableFuture!";
});

// Add a callback to handle the result
future.thenAccept(result -> System.out.println(result));

In this example, we create a CompletableFuture using supplyAsync, which is similar to applyAsync but does not take in any arguments. We pass in a lambda that computes a string and returns it.

We then add a callback to the CompletableFuture using thenAccept. This callback takes in the result of the CompletableFuture and prints it out to the console.

By using applyAsync or supplyAsync, we can easily create CompletableFutures that perform computations asynchronously and handle the results in a callback. This makes it easier to write asynchronous and concurrent code in Java.