Is there a way to convert this iterative function that takes a Collection of Integer objects and adds these elements, into a recursive one?

Originally, we were encouraged to solve the problem with recursion, but so far I can only think of an interative one.

import java.util.*;

public class Problem1 {

	static Integer add(Collection integers) {
		Integer sum = 0;
	
		Iterator iterator = integers.iterator();		
	
		while (iterator.hasNext()) {
			
			sum = sum + (Integer) iterator.next();
		}
		return sum;
		
	}
}

One way to do it is to use then remove the elements as you recurse through using an iterator.

public class Problem1 {    
    static Integer add(Collection integers) {
        Integer sum = 0;
        Iterator it = integers.iterator();
    
        if (!it.hasNext()) {
            return 0;
        }
        Integer number = (Integer)it.next();
        it.remove();
        sum += number + add(integers);

        return sum;
    }
}

Try this.

static Integer add(Iterator it) {
    if (!it.hasNext())
        return 0;
    else
        return (Integer)it.next() + add(it);
}

static Integer add(Collection integers) {
    return add(integers.iterator());
}

and

Collection integers = List.of(1, 2, 3, 4);
System.out.println(add(integers));

output

10