iterator 迭代器

一个接口 方便各个集合之间进行数据查找操作 类似指针形式 这里看一个ArrayList实现方式

/**
     * Returns an iterator over the elements in this list in proper sequence.
     *
     * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
     *
     * @return an iterator over the elements in this list in proper sequence
     */
    public Iterator<E> iterator() {
        return new Itr();
    }

  public boolean hasNext() {
            return cursor < limit;
        }

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

提供了一系列增删改查操作 看起来实现方式类似指针