イテレータのサンプル

iterator_sample.rs

use std::iter::Iterator;

struct FibonacciNumberGenerator {
    n: [u128; 2],
}

impl FibonacciNumberGenerator {
    fn new() -> Self {
        FibonacciNumberGenerator { n: [0, 1] }
    }
}

impl Iterator for FibonacciNumberGenerator {
    type Item = u128;
    fn next(&mut self) -> Option<Self::Item> {
        // それぞれ1/2して足したらu128の1/2のMAX越える=1/2しなくても超えるのでNoneを返す。
        if self.n[0] / 2 + self.n[1] / 2 < u128::MAX / 2 {
            let n = self.n[0] + self.n[1];
            self.n[0] = self.n[1];
            self.n[1] = n;
            Some(n)
        } else {
            None
        }
    }
}

fn main() {
    let fib = FibonacciNumberGenerator::new();
    for number in fib {
        print!("{} ", number);
    }
}

IteratorSample.java

import java.util.Iterator;
class IteratorSample {
    public static void main(String[ ] args) {
        FibonacciNumberGenerator fib = new FibonacciNumberGenerator();
        for(int n: fib){
            System.out.println(n+" ");
        }
    }
}

class FibonacciNumberGenerator implements Iterable<Integer>,Iterator<Integer>{
    int[] n = new int[2];
    public FibonacciNumberGenerator(){
        this.n[0]=0;
        this.n[0]=1;
    }
    public Iterator<Integer> iterator() {
        return this;
    }

    public boolean hasNext(){
        if (this.n[0]/2 + this.n[1]/2 < Integer.MAX_VALUE/2){
            return true;   
        }
        return false;
    }
    public Integer next(){
        int n = 0;
        if (this.hasNext()){
            n = this.n[0] + this.n[1];
            this.n[0] = this.n[1];
            this.n[1] = n;
        }
        return n;
    }
}