Java Streams Api, finite stream [duplicate]

Question

I'm trying to create a fibonacci sequence through the usage of Java Streams API. I've create a supplier, but I want it to stop at a specific value (e.g 1000000).

The suplier:

import java.util.function.Supplier;

public class FibonacciSupplier implements Supplier<Integer> {

    private int current;
    private int next;

    public FibonacciSupplier() {
        current = 0;
        next = 1;
    }

    @Override
    public Integer get() {
        int result = current;
        current = next + current;
        next = result;
        return result;
    }
}

How I would like it to be:

Stream.generate(new FibonacciSupplier()).maxValue(1000000);

The maxValue does not exist as a function, I'm using it as a name to for context.

Have you tried using an if statement? if (value > 1000000) { dontDo(); }? — Frontear
– Frontear, Commented Nov 7, 2018 at 17:29

ernest_k · Accepted Answer · 2018-11-07 17:43:14Z

3

The best solution is to use takeWhile, which is available in Java 9+:

Stream.generate(new FibonacciSupplier())
    .takeWhile(i -> i <= 1000000) //will stop stream when value exceeds given limit
    .forEach(System.out::println);

If you're using Java 8, then you may want to look into hacks for stopping an infinite stream

answered Nov 7, 2018 at 17:43

ernest_k

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1 Comment

Michael Over a year ago

If you knew that question existed, why didn't you close this as a dupe?

Nicholas K · Accepted Answer · 2018-11-07 17:34:19Z

0

You'll need to use the .limit() method on the stream as below :

Stream.generate(new FibonacciSupplier()).limit(1000).forEach(System.out::println);

From the docs,

Returns a stream consisting of the elements of this stream, truncated to be no longer than {@code maxSize} in length.

answered Nov 7, 2018 at 17:34

Nicholas K

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2 Comments

kofemann Over a year ago

takeWhile from java9 will do the job

Michael Over a year ago

Eh... Yes and no. limit limits by the number of elements. He wants to stop once the sequence has exceeded a certain value. How do you know that a fib number of 1000000 is element 1000?

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