为什么删除操作报错？

for(Cat cat:set) {
			if("花花02".equals(cat.getName())) {
				set.remove(cat);
			}
		}

Exception in thread "main" java.util.ConcurrentModificationException

at java.util.HashMap$HashIterator.nextNode(Unknown Source)

at java.util.HashMap$KeyIterator.next(Unknown Source)

at com.imooc.set.CatTest.main(CatTest.java:73)