Is there a way to stop Stream.iterate() with a predicate?

Question

In the web I found only one way to stop the iterate method. By using the limit() function. But that iterates a concreate ammount of loops. I want use for the halt a predicate.

...
Stream.iterate(0, i -> i*2).while(i -> i < MAX)
...

Is there a way to do it with Streams?

Update 1 : Java 8 is used

@RavindraRanwala I want to implement a Stream that calculates Fibbonacies that are smaller than a certain number — DIBits, Feb 08 '19 at 10:09
Show us your input and expected output. There may be better ways of doing this. People can't answer a question without knowing it's context properly. — Ravindra Ranwala, Feb 08 '19 at 10:10

Naman · Accepted Answer · 2019-02-08T10:17:12.433

10

Using Java-9 or above, one way is to use Stream.takeWhile as:

Stream.iterate(1, i -> i * 2) // notice identity value in seed
      .takeWhile(i -> i < MAX)

Another alternative is to use Stream.iterate

Stream.iterate(1, i -> i < MAX, i -> i * 2)

edited Feb 08 '19 at 10:17

answered Feb 08 '19 at 10:07

Naman

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Perhaps worth mentioning that this was added in Java 9. – Andy Turner Feb 08 '19 at 10:07
is there any alternate for Stream.iterate.takeWhile() in Java-8 – Ashok Kumar N Feb 08 '19 at 10:11
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Its a cool way to do it. Thanks. But I am using Java 8. I will update my question – DIBits Feb 08 '19 at 10:12
The third parameter in `iterate` is not really an alternative to `takewhile`, though, as `takewhile` can e.g. be applied after a `map` step. Of course, for OP's case it may be fine. – tobias_k Feb 08 '19 at 10:22
@tobias_k well true, specific to dealing with integers currently. More likely towards the `IntStream` if I could say so. – Naman Feb 08 '19 at 10:29
Are there any differences, performance-wise, between the two approaches? – Marinos An Jul 14 '20 at 15:06

Is there a way to stop Stream.iterate() with a predicate?

1 Answers1