I was recently taking the UCB CS70B course and following the code example of iterator in the lecture video: https://www.youtube.com/watch?v=AKnMv0ootkg&list=PL8FaHk7qbOD4vPE_Bd8QagarKi3kPw8rB&index=5
I followed the video to write the following Java code:

import java.util.*;

public class ArraySet<T> implements Iterable<T>{
    private T[] items;
    private int size;
    public ArraySet() {
        items=(T[]) new Object[100];
        size=0;
    }

    /* Returns true if this map contains a mapping for the specified key.
     */
    public boolean contains(T x) {
        for (int i=0;i<size;i+=1){
            if (items[i]==null){
                if (x==null){
                    return true;
                }
            }
            if (x.equals(items[i])){
                return true;
            }
        }
        return false;
    }

    /* Associates the specified value with the specified key in this map.
       Throws an IllegalArgumentException if the key is null. */
    public void add(T x) {
        if (x==null){
            throw new IllegalArgumentException("Cannot add null to ArraySet");
        }

        if (contains(x)){
            return;
        }
        items[size]=x;
        size+=1;
    }

    /* Returns the number of key-value mappings in this map. */
    public int size() {
        return size;
    }

    //returns an iterator into ME
    @Override
    public Iterator<T> iterator(){
        return new ArraySetIterator();
    }

    private class ArraySetIterator implements Iterator<T>{
        private int wizPos;
        public ArraySetIterator(){
            wizPos=0;
        }
        public boolean hasNext(){
            return wizPos<size;
        }
        public T next(){
            T returnItem=items[wizPos];
            wizPos+=1;
            return returnItem;
        }
/*
        @Override
        public String toString(){
            StringBuilder returnSB=new StringBuilder("{");
            for (int i=0;i<size;i+=1 ) {
                returnSB.append(items[i]);
                returnSB.append(",");
            }
            returnSB.append("}");
            return returnSB.toString();
        }
*/
        @Override
        public String toString(){
            List<String> listOfItems=new ArrayList<>();
            for (T x:this){
                listOfItems.add(x.toString());
            }
        String.join(",",listOfItems);
            return "{"+String.join(",",listOfItems);
        }


        @Override
        public boolean equals(Object o){//overriding equals always input Object
            if (o instanceof ArraySet oas){
                if (oas.size!=size){
                    return false;
                }
                for (T x:this){
                    if (!oas.contains(x)){
                        return false;
                    }
                }
            }
            return true;
        }

        public static<Glerp> ArraySet<Glerp> of(Glerp...stuff){
            ArraySet<Glerp> returnSet=new ArraySet<Glerp>();
            for (Glerp x: stuff){
                returnSet.add(x);
            }
            return returnSet;
        }



    }

    public static void main(String[] args) {
        ArraySet<String> s = new ArraySet<>();
        s.add("horse");
        s.add("fish");
        s.add("house");
        s.add("fish");
        System.out.println(s.contains("horse"));
        System.out.println(s.size());

        ArraySet<Integer> aset=new ArraySet<>();
        aset.add(5);
        aset.add(55);
        aset.add(789);

        for (int i:aset){
            System.out.println(i);
        }
    }

In this code, I got public class ArraySet<T> implements Iterable<T> and wrote the method public Iterator<T> iterator() and private class ArraySetIterator implements Iterator<T>, just like the video has done. But when I write toString() method and equals() method, the instructor wrote for (T x:this) and works fine, but my code in IDEA showed “Foreach not applicable to type ‘ArraySet.ArraySetIterator'” for both for (T x:this) and IDEA suggests me to change to for (ArraySetIterator it = this; it.hasNext(); ) . So I am asking why this is happening and why the instructor could do it perfectly but mine couldn’t?

I googled around and asked ChatGPT but none of them provided answers as if this should not happen at all. All I found was this:foreach not applicable to expression type
which did not implements iterable and override Iterator