如何将数组列表中的特定项移动到第一项 [英] How to move specific item in array list to the first item

问题描述

例如:一个列表

A B C D E

给定 C ，切换到

C A B D E

注意数组大小会发生变化，有些项目可能会在运行时删除

Notice that the array size will change, some items may removed in run times

Collections.swap(url, url.indexOf(itemToMove), 0);

此语句不起作用，因为它输出的是 C B A D E 而不是 C A B D E ，如何解决?

This statement is not working because it output C B A D E not C A B D E , how to fix it?

谢谢.

推荐答案

你想要的是 ArrayList 中的一个非常昂贵的操作.它需要将列表开头和 C 位置之间的每个元素向下移动一个.

What you want is a very expensive operation in an ArrayList. It requires shifting every element between the beginning of the list and the location of C down by one.

但是，如果您真的想这样做:

However, if you really want to do it:

int index = url.indexOf(itemToMove);
url.remove(index);
url.add(0, itemToMove);

如果这对您来说是一个频繁的操作，而随机访问的频率则较低，您可以考虑切换到另一个 List 实现，例如 LinkedList.如果您非常关心元素的顺序，您还应该考虑列表是否是正确的数据结构.

If this is a frequent operation for you, and random access is rather less frequent, you might consider switching to another List implementation such as LinkedList. You should also consider whether a list is the right data structure at all if you're so concerned about the order of elements.

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