completablefuture interview questions

• What is CompletableFuture? …
• Can you explain what a completion stage is? …
• How do you create a completable future in Java? …
• Does creating an instance of CompletableFuture automatically start its execution?

Java | Future vs CompletableFuture | Interview Question | Senior Java Developer | Lead Developer

So What’s New in CompletableFuture?

CompletableFuture extends Future and makes it… completable. This is a big deal, considering that Future objects were limited before Java 8, with only 5 methods available.

This new and improved CompletableFuture has 2 main benefits:

Back to our simple example, let’s say that Marvel’s API didn’t return a timely result, and getMarvelHeroWithCharacter() is still processing, taking it’s time, while we’re already done with everything else that we wanted to do in the meantime. Assuming we don’t want to wait (for our lives to be over), a CompletableFuture can help us return an intermediate result. Like… Mystique, since at the worst case she can shapeshift into any other superhero.

You can also create a completed CompletableFuture in advance that returns a known value. That might come in handy in your testing environment, in case you’ll want to combine that known value with one that needs to be computed:

Tens of other more useful methods are available and they include transforming and acting on one CompletableFuture (thenApply), running code on completion (thenAccept/thenRun), combining two CompletableFuture together and more. For a complete guide we recommend you to read Java 8: Definitive guide to CompletableFuture.

If you’re using Guava or Scala (with its Futures), this new feature might sound familiar. It’s similar to Guava’s ListenableFuture, which defines a consistent API for Future objects to register completion callbacks.

Similarly to the new CompletableFuture, the ability to add a callback allows responding to incoming events in an asynchronously and effective way. You can register callbacks to be executed when a computation is complete, and support many operations that the basic Future interface can’t support.

When the Going Gets Tough

Using CompletableFuture gives us the ability to run along with our code without having to wait for the results, but it still can’t promise your code won’t break while running in production. When errors occur, you’ll need to to identify and analyze them as quickly as you can to deploy a hotfix.

For these kind of situations, Takipi will enable you to fix issues in your code effectively when they arise, without having to “wait” until someone else run into them.

CompletableFuture fits right in as part of the asynchronous programming trend, that became popular during the past few years. It’s no wonder everyone’s talking about it, since we can use it to run a number of tasks at the same time, which allow an optimal workflow.

In case you’re already a fan of asynchronous programming, you might want to check out our post about 7 Reactive Programming Tools You MUST Know.

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What new features did Java 8 introduce?

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Java 8 Interview Questions – Basic Level

Here are some Java8 interview questions to get us warmed up.

FAQ

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