Can't pass 2nd requirement. Stuck at the remove() method ...

Question about the task

Circular iterator

Java Collections, Level 7, Lesson 4

Under discussion

I've been trying a couple of things without success

The Solution class inherits ArrayList.
Properly override the iterator method in the Solution class.
Write your own CircularIterator class inside the Solution class. It will be an iterator for the Solution list.
The iterator must move circularly through all of the elements.
In all other ways, its behavior must be identical to the current iterator.

Requirements:

The circular iterator must go to the first element after the last element and so on.
The no-argument remove method must remove the current element.
If the list is modified incorrectly from different threads, a ConcurrentModificationException must be thrown.
The Solution class must be a child of the ArrayList class.
The Solution class's iterator() method must return a CircularIterator object.

package com.codegym.task.task37.task3701; import java.util.*; /* Circular iterator */ public class Solution<T> extends ArrayList<T> { public static void main(String[] args) { Solution<Integer> list = new Solution<>(); list.add(1); list.add(2); list.add(3); int count = 0; for (Integer i : list) { //1 2 3 1 2 3 1 2 3 1 System.out.print(i + " "); count++; if (count == 10) { break; } } } public Iterator<T> iterator() { return new CircularIterator(); } public class CircularIterator implements Iterator<T> { int size = Solution.this.size(); int currentPointer; int lastRet = -1; int expectedModCount = modCount; public CircularIterator(){ currentPointer = 0; } public boolean hasNext() { return (true); } public T next() { checkForComodification(); if (currentPointer >= size) { lastRet = currentPointer; currentPointer = 0; } else{ lastRet = currentPointer; } return Solution.this.get(currentPointer++); } public void remove(){ checkForComodification(); if (lastRet < 0) { throw new IllegalStateException(); } Solution.this.remove(lastRet); if (lastRet < size()-1) currentPointer = lastRet; lastRet = -1; expectedModCount = modCount; } final void checkForComodification() { if (expectedModCount != modCount) throw new ConcurrentModificationException(); } } }

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Marcin Olech

Level 41 , Kraków, Poland

22 February 2020, 09:56

There is no need to play with indexes and modCounter. Solution extends ArrayList class so why do not use ArrayList methods (including ArrayList.iterator() method itself) and delegate CircularIterator methods calls to ArrayList iterator? (I'm not sure if that sounds clear so let me show the code):

//CircularIterator class
Iterator<T> iterator = Solution.super.iterator();
int cursor = 0;

These are only two fields you need:) And implement methods hasNext(), next(), remove(), forEachRemaining (delegate the calls to iterator field and some simple play with cursor)