14- Waiting for Many Tasks to Complete

Jul 04, 2026 01:18 · 2:48 · English · Whisper Turbo · 2 Đầu ghi

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Sometimes we need to wait for the completion of many tasks before doing something else.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Let me show you how to do this.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

So I'm going to create three completable features to represent three

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

asynchronous tasks.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Here's the first one.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

We set this to completable future that supply sync

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and here we return one.

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Here's our second task.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

We return two and here's the third task.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Now, we want to wait for all these tasks to complete before doing something else.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

To do that we call completable future dot all

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

of.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

Now look at the signature of this method.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Here we have completable future dot dot dot.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

This is called var args which means a variable number of arguments.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

We can pass zero or more arguments.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

So I'm going to pass first,

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

second,

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

and third.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Now this will return a new completable future that will complete when

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

all of these completable futures complete.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

So let's store the result over here.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Look at the type of this variable that is a completable future

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

of void.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Why is it void?

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Because each completable future may return a different data type,

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

one might return a string,

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

another completable future might return an integer.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

So there is no way for us to know what is the final result.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

That is why this is a completable future of void.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

It's like a task that will complete when many other tasks complete.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

Okay?

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

So,

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

here we can write all dot then run,

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

here we pass a runnable object,

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

and then print

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

all tasks completed successfully.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

Let's run our program.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

So here's the message.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

But what if you want to get the result of each of these completable future

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

objects?

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

Well, that is very easy.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

We can call first that get this will return the

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

result of the first completable future.

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

But in this case,

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

this method is not going to block the current thread because this code

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

this task is going to get executed asynchronously when

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

all these tasks are complete.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

So at this point,

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

when we call the get method on any of these completable features,

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S… Speaker 2 (14- Waiting for Many Tasks to Complete)

we get the result immediately because the result is ready.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

So we get the result of the first task and store

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

it here.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

First result.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

Now we should wrap this inside a try catch block.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

So we get the first result and then print it.

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S… Speaker 1 (14- Waiting for Many Tasks to Complete)

So here's the first result and our final message.

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