Java 8 Stream, getting head and tail

Question

Java 8 introduced a Stream class that resembles Scala\'s Stream, a powerful lazy construct using which it is possible to do something like this very concisely:

Answer 1

To get head and tail you need a Lazy Stream implementation. Java 8 stream or RxJava are not suitable.

You can use for example LazySeq as follows.

Lazy sequence is always traversed from the beginning using very cheap first/rest decomposition (head() and tail())

LazySeq implements java.util.List interface, thus can be used in variety of places. Moreover it also implements Java 8 enhancements to collections, namely streams and collectors

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package com.company;

import com.nurkiewicz.lazyseq.LazySeq;

public class Main {

    public static void main(String[] args) {

        LazySeq ints = integers(2);
        LazySeq primes = sieve(ints);
        primes.take(10).forEach(p -> System.out.println(p));

    }

    private static LazySeq sieve(LazySeq s) {
        return LazySeq.cons(s.head(), () -> sieve(s.filter(x -> x % s.head() != 0)));
    }

    private static LazySeq integers(int from) {
        return LazySeq.cons(from, () -> integers(from + 1));
    }

}