你有两个问题。

第一个问题 - 为什么你得到 ConcurrentModificationException - 是因为你正在使用列表删除元素，而不是迭代器。

The first issue - why you're getting ConcurrentModificationException - is because you're using the list to remove elements, not the iterator.

您必须使用 it.remove（）删除您当前所在的元素。

You must use it.remove() to remove the element you're currently on.

接下来，您要将字符串与 == 进行比较 - 这根本不能保证。您应该使用 .equals 。

Next, you're comparing strings with == - this isn't guaranteed to work at all. You should be using .equals instead.

反转您比较它们的顺序，这样您就不会运行也有机会获得 NullPointerException 。

Reverse the order you compare them against so you don't run a chance of getting a NullPointerException there, too.

以下是块的外观，重新访问。

Here's what the block looks like, revisited.

public static void main(String[] args) {
    Box b = new Box();
    ArrayList<Pencil> box = b.list;
    for(Iterator<Pencil> it = box.iterator(); it.hasNext();) {
        Pencil p = it.next();
        if ("black".equals(p.getColor())) {
            it.remove();
        }
    }
}