Almost there, stuck on the 3rd condition

Question about the task

Under discussion

I think I have used try/catch for every place where an index out of bounds exception might occur. Not sure what else to do.

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; } } } @Override public Iterator<T> iterator() { return new CircularIterator(); } public class CircularIterator implements Iterator<T> { int nextIndex = 0; int removalIndex = 0; @Override public boolean hasNext() { return size() > 0; } @Override public T next() { if(nextIndex >= size()) { nextIndex = 0; } removalIndex = nextIndex; try { return (T) Solution.this.toArray()[nextIndex++]; } catch(Exception e) { throw new ConcurrentModificationException(); } } @Override public void remove() { try { Solution.this.remove(removalIndex); } catch(Exception e) { throw new ConcurrentModificationException(); } } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

3 February 2023, 19:08

Here is the code inside the Iterator class implemented inside the ArrayList class:

private class Itr implements Iterator<E> {
int cursor;       // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;

// prevent creating a synthetic constructor
Itr() {}

public boolean hasNext() {
   return cursor != size;
}

@SuppressWarnings("unchecked")
public E next() {
   checkForComodification();
   int i = cursor;
   if (i >= size)
      throw new NoSuchElementException();
   Object[] elementData = ArrayList.this.elementData;
   if (i >= elementData.length)
   throw new ConcurrentModificationException();
   cursor = i + 1;
   return (E) elementData[lastRet = i];
}

public void remove() {
   if (lastRet < 0)
      throw new IllegalStateException();
   checkForComodification();

   try {
      ArrayList.this.remove(lastRet);
      cursor = lastRet;
      lastRet = -1;
      expectedModCount = modCount;
   } catch (IndexOutOfBoundsException ex) {
      throw new ConcurrentModificationException();
   }
}

@Override
public void forEachRemaining(Consumer<? super E> action) {
   Objects.requireNonNull(action);
   final int size = ArrayList.this.size;
   int i = cursor;
   if (i < size) {
      final Object[] es = elementData;
      if (i >= es.length)
         throw new ConcurrentModificationException();
      for (; i < size && modCount == expectedModCount; i++)
         action.accept(elementAt(es, i));
   // update once at end to reduce heap write traffic
   cursor = i;
   lastRet = i - 1;
   checkForComodification();
   }
}

final void checkForComodification() {
   if (modCount != expectedModCount)
      throw new ConcurrentModificationException();
   }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

3 February 2023, 19:08

I would expect you could copy most, if not all, of this and modify it to the task's specifications.