面试官不按套路出牌，上来就让聊一聊Java中的迭代器(Iterator )，夺命连环问，怎么办？

public interface Iterator<E> {
    //是否有下一个元素
 boolean hasNext();
  
 //下一个元素
 E next();
  
 //从迭代器指向的集合中删除迭代器返回的最后一个元素
 default void remove() {
     throw new UnsupportedOperationException("remove");
 }
  
 //遍历所有元素
 default void forEachRemaining(Consumer<? super E> action) {
     Objects.requireNonNull(action);
     while (hasNext())
         action.accept(next());
 }
}

public class Test {
    public static void main(String[] args) {
        ArrayList<String> str = new ArrayList<>();
        str.add("aaa");
        str.add("bbb");
        str.add("ccc");
        //迭代器遍历
        Iterator it = str.iterator();
        while (it.hasNext()) {
            System.out.print(it.next() + "，");
        }
    }
}

aaa，bbb，ccc，

public interface Collection<E> extends Iterable<E> {
 ...
 Iterator<E> iterator();
 ...

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;

        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
        @SuppressWarnings("unchecked")
        public void forEachRemaining(Consumer<? super E> consumer) {
            Objects.requireNonNull(consumer);
            final int size = ArrayList.this.size;
            int i = cursor;
            if (i >= size) {
                return;
            }
            final Object[] elementData = ArrayList.this.elementData;
            if (i >= elementData.length) {
                throw new ConcurrentModificationException();
            }
            while (i != size && modCount == expectedModCount) {
                consumer.accept((E) elementData[i++]);
            }
            // update once at end of iteration to reduce heap write traffic
            cursor = i;
            lastRet = i - 1;
            checkForComodification();
        }

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

for (String str : list) {
    System.out.print(str + "，");
}

Iterator var3 = list.iterator();

while(var3.hasNext()) {
    String str = (String)var3.next();
    System.out.print(str + "，");
}

public interface ListIterator<E> extends Iterator<E> {
    boolean hasNext();
    E next();
    boolean hasPrevious();
    E previous();
}