7- Creating a Completable Future

Jul 03, 2026 23:04 · 3:42 · English · Whisper Turbo · 2 वक्ता:

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This completable future class has a couple of methods that we use for creating a

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completable future object.

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If you want to run a task that doesn't return a value we call run async.

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This basically says run this task in an asynchronous or non

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-blocking fashion.

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Here we can pass a runnable object or

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a runnable plus an executor.

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If you don't pass an executor,

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this method is going to run our task on a common pool.

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Let me show you.

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So here we have this class fork join pool.

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This is one of the implementations of the executor service interface.

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Now here we have a static method common pool and this

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returns the pool that is used by the completable future class.

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So if you don't supply a pool,

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this is the pool that is going to be used under the hood.

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Now this pool is well aware of the number of available threads.

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Earlier I told you how to get that.

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So we have this class runtime.

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we call it get runtime and then available processors.

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So on my machine I have four cores and each core has two threads.

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So the common pool is based on the number of available threads.

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Now if this doesn't fit your application,

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you can always create a custom pool with fewer or more threads.

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Okay, now to simplify this,

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I'm not going to pass a pool,

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I'm just going to pass a runnable object.

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So let's create a runnable object called task.

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And here we just want to print something.

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Now we can pass the task over here.

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Now this returns a completable future object.

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Now look at the type of this object.

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It's a completable future of void.

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Because our task is not returning a value.

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Okay?

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Now

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With this single line of code,

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we can execute a task in an asynchronous fashion.

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We didn't have to create an executor and then submit a task to it

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and then shut it down.

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We only call completable future that run async.

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If our task would return a value instead of calling the run async

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method, recall the supply async method.

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Now look at the signature of this method.

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Here we can pass a supplier

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That is a functional interface.

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We talked about it before.

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It has a single abstract method called get that returns a value.

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Now similar to the run async method,

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here we can pass a supplier or a supplier plus an

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executor.

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If we don't supply an executor,

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the common pool will be used.

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Okay, so I'm going to change this task to a supplier

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of integer and here let's

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just return one.

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this will return a completable future of integer.

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Let me show you.

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So the type of this future object

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is completable future of integer.

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Now,

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if you want to get this value,

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we call future .get because this is a future object.

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So all the methods that you learn about future objects also exist here.

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As I told you before,

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this get method is a blocking method.

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So it's going to block the current thread until the result is ready.

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But in this completable future object,

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we have a bunch of other methods that allow us to build complex asynchronous

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operations.

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We'll talk about them as you go through this section.

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Now let's call the get method and store the result

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over here.

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We should wrap this with a try catch block and

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then print the result.

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There you go.

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So this is how we can create a completable feature object.

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