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explain what iterator is in algorithms?

public class IteratorToSkipZero {

int current;
int[] list;

public static void main(String[] args) {
int[] input = {1,0,0,0,0,6,0};
IteratorToSkipZero it = new IteratorToSkipZero(input);
System.out.println(it.next());
System.out.println(it.next());
System.out.println(it.hasNext());
}

public IteratorToSkipZero(int[] l){
list = l;
current = 0;
}

public boolean hasNext(){
skipZero();
if(current == (list.length)){
return false;
}
return true;

}

public int next(){

int o = 0;
if(hasNext()){
o = list[current];
current++;
return o;
}
throw new UnsupportedOperationException();

}

private void skipZero() {
while(current < list.length){
if(list[current] == 0){
current ++;
} else {
break;
}
}
}
}

package com.test.integer;

public class GreaterThanZeroIntIterator {
private int[] intValues;

private int curIndex = 0;

private boolean hasNext = false;

public GreaterThanZeroIntIterator(int[] intValues) {
super();
this.intValues = intValues;

fetchNext();
}

public static void main(String[] args) {
int[] intArr = new int[] { 1, 2, 3, 0, 1, 2, -3 };

GreaterThanZeroIntIterator it = new GreaterThanZeroIntIterator(intArr);
while (it.hasNext()) {
System.out.println(it.next());
}

}

public boolean hasNext() {
return hasNext;
}

public int next() {
int result = intValues[curIndex++];
fetchNext();

return result;
}

private void fetchNext() {
hasNext = false;

while (curIndex < intValues.length) {
if (intValues[curIndex] != 0) {
hasNext = true;
break;
} else {
curIndex++;
}
}
}
}

public class IntegerStream  implements Iterable{

    private Node head;

    @Override
    public Iterator iterator() {
        return null;
    }

    class Node{

        private Integer data;
        private Node next;
    }

    class IntegerStreamIterator implements Iterator {

        Node curr = head;
        @Override
        public boolean hasNext() {
            return curr != null;
        }

        @Override
        public Object next() {
            while(curr.data == 0){
                curr = curr.next;
            }
            Integer item = curr.data;
            curr = curr.next;
            return item;
        }
    }
}