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Lesson 12 - Multithreading in Java - CompletableFuture

In the previous lesson, Multithreading in Java - ForkJoinPool, we talked about ForkJoinPool. In this lesson, we're going to learn what is in my opinion the best class for parallel programming offered by the basic Java Concurrency framework - CompletableFuture.

A few lessons back, we introduced different interfaces related to parallel programming: Runnable, Callable, and Future. The interfaces are ordered according to the increasing functionality. We described the Future interface as an object that will contain the result of a task sometime in the future. The problem with this interface is that we don't know when the result will be available. The only way to get the result is to use the blocking get() method, which blocks the thread in which it's called. The developers tried to solve this problem by using the CompletableFuture class and I must say that they did great. Let's introduce CompletableFuture.


Right at the beginning I have to say that if you know something about reactive programming, you will feel at home. Alternatively, you can find many similarities to the promises from JavaScript.

The class implements two interfaces:


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In this tutorial, we'll introduce advanced techniques for parallel programming in Java. Let's describe CompletableFuture.

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Article has been written for you by Petr Štechmüller