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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: Re: getFibonacciArray() cannot call getFibonacciArray(int from)
Date: Sat, 03 Aug 2019 11:11:32 +0200
Organization: Decebal Computing
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Cecil Westerhof <Cecil@decebal.nl> writes:

> When I turn it into a class it becomes really strange. I changed the
> code to:
>     import java.util.stream.LongStream;
>     import java.util.stream.Stream;
>
>
>     class Fibonacci {
>         long[] getFibonacciArray() {
>             // return getFibonacciArray(0);
>             return getFibonacciStreamFrom(0).toArray();
>         }
>
>         long[] getFibonacciArray(int from) {
>             return getFibonacciStreamFrom(from).toArray();
>         }
>
>         long[] getFibonacciArray(int from, int to) {
>             // check parameters
>             int count = to - from;
>             return getFibonacciStreamFrom(from).limit(count).toArray();
>         }
>
>         // Needs at least Java 9 because we use a predicate in the iterator
>         // Index 0 of stream i element always contains fibonacci(i) and
>         // index 1 always contains fibonacci(i + 1)
>         // So the map makes sure you have the fibonacci number
>         LongStream getFibonacciStream() {
>             return Stream.
>                 iterate(new long[]{0, 1}, t -> t[0] >= 0, t -> new long[]{t[1], t[0] + t[1]})
>                 .mapToLong(t -> t[0]);
>         }
>
>         LongStream getFibonacciStreamFrom(int from) {
>             // Check parameter
>             return getFibonacciStream().skip(from).map(l -> l);
>         }
>     }
>
> When compiling this, I get:
>     Fibonacci.java:26: error: method iterate in interface Stream<T#2> cannot be applied to given types;
>             return Stream.
>                          ^
>       required: T#1,UnaryOperator<T#1>
>       found: long[],(t)->t[0] >= 0,(t)->new l[...]t[1]}
>       reason: cannot infer type-variable(s) T#1
>         (actual and formal argument lists differ in length)
>       where T#1,T#2 are type-variables:
>         T#1 extends Object declared in method <T#1>iterate(T#1,UnaryOperator<T#1>)
>         T#2 extends Object declared in interface Stream
>     1 error

This was because jshell was using Java 9, and the compiler Java 8.
This is Java 9 functionality, but the error message was not clear. I
have both updated to 11.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof