Choosing between thenApply and thenApplyAsync in CompletableFuture

Java’s CompletableFuture class provides two key methods, thenApply and thenApplyAsync, for processing the results of asynchronous computations. While both methods serve the same purpose, their subtle differences can significantly impact the performance and concurrency of your program. This article explores the distinctions between thenApply and thenApplyAsync, offering insights into when to use each based on the specific requirements of your application.

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`thenApply` and `thenApplyAsync` are both methods in Java’s CompletableFuture class, and they’re used to process the result of a computation when it becomes available. However, there are key differences between them that can impact the performance and behavior of your program.

1. Execution Thread: The main difference between `thenApply` and `thenApplyAsync` is the thread they’re executed on. `thenApply` executes the callback function on the same thread that completed the previous CompletableFuture, while `thenApplyAsync` executes the callback function on a different thread obtained from the ForkJoinPool.commonPool() (default) or a given Executor.

2. Non-blocking: `thenApplyAsync` is non-blocking. It can offload the subsequent completion stage to some other thread, allowing the current thread to do other work in the meantime. This is beneficial in highly concurrent programs where you want to make the best use of your system’s resources.

3. Performance: In terms of performance, `thenApplyAsync` can be more efficient when the callback function is a long-running task, as it doesn’t block the main thread. However, if the task is short and fast, `thenApply` might be preferable as it avoids the overhead of creating a new task and scheduling it to run on a different thread.

let’s consider a real-world scenario: an online shopping system.

In this system, when a user places an order, several steps occur:

1. The order details are saved in the database.
2. An email confirmation is sent to the user.
3. The order is sent to the warehouse for packaging and delivery.

Each of these steps could be represented by a CompletableFuture, and they could be chained…