Design patterns: Iterator pattern

Question

    public BigDecimal next() {

        for (int i = 1; i < 100; i++) {
            BigDecimal cur = new BigDecimal(1);
            BigDecimal prev = new BigDecimal(0);

            final BigDecimal next = cur.add(prev);
            prev = cur;
            cur = next;
        }

        return cur;
    }

Could not implement Bigdecimal in this for loop to get Fibonacci numbers

Answer 1

In your code, hasNext is always false. This tells the consumer of the iterator that we reached the end of the iteration.

Answer 2

This is what you want to achieve

I replaced all BigDecimal references with Integer. If you want to keep as it then needs to make some small changes.

//This is class with main method
import java.util.Iterator;

public class IteratorPattern {
public static void main(String[] args) {
    int n = 10;
    FibonacciSequence fibonacciSequence = new FibonacciSequence(n);

    System.out.println("iteration using iterator for-loop");

    //iteration using iterator for-loop
    for (Integer fibonacciNumber : fibonacciSequence) {
        System.out.println(fibonacciNumber);
    }

    System.out.println("iteration using iterator");

    //iteration using iterator
    Iterator<Integer> iterator = fibonacciSequence.iterator();
    while (iterator.hasNext()) {
        System.out.println(iterator.next());
    }
}
}

class FibonacciSequence implements Iterable<Integer>, Iterator<Integer> {

private final Integer n;
private Integer a;
private Integer b;
private int c = 1;

FibonacciSequence(Integer n) {
    this.n = n;
}

@Override
public Iterator<Integer> iterator() {
    return new FibonacciSequence(n);
}

@Override
public boolean hasNext() {
    return c <= n;
}

@Override
public Integer next() {
    c++;
    if (a == null && b == null) {
        a = 0;
        return 0;
    } else if (b == null) {
        b = 1;
        return b;
    } else if (a == 0 && b == 1) {
        a = 1;
        return b;
    }
    Integer temp = b;
    b = b + a;
    a = temp;
    return b;
}
}

Output:

 iteration using iterator for-loop
0
1
1
2
3
5
8
13
21
34
iteration using iterator
0
1
1
2
3
5
8
13
21
34

Now the point is what changes I made.

1. As told by @Tom S. your hasNext method should return false if the count reaches to n.

2. I changed logic in the next method. Take a look at it.