使用 ArrayList 或 HashMap 提高速度 [英] Using ArrayList or HashMap for better speed

问题描述

我需要对象 A 的列表"或地图"....此列表将从另一个 ArrayList 添加.当 A 的 id 参数等于对象 A 时，认为对象 A 等于另一个.

I need a 'List' or 'Map',... of object A. This list will be added from another ArrayList. Object A is considered to be equal to another when id parameter of A equals.

我的问题是我只想添加一个不存在于我的列表中的对象.我想知道两种实施方案之间的差异.使用 ArrayList 或 HashMap

My problem is I only want add an object that does not exist in my List. I wonder between the two alternatives for implementation. Using ArrayList or HashMap

1. ArrayList:

for (A a: source) {if (! (a in ArrayList)) addToArrayList();}

2. HashMap <id, A>

for (A a: source) {hasmap.put (a.id, a)}

哪个可以更快地添加大量(超过 1000 个对象，或更多的对象)我的问题有更好的模式吗???

Which will give better speed to add a large number (over 1000 objects, or bigger number of object) Is there a better pattern for my problem???

推荐答案

首先，我要大胆声明这是两种完全不同的数据结构. A List 处理元素的线性表示，而 Map 处理键对值.

First, I'm going to go out on a limb and state that these are two completely different data structures. A List deals with a linear representation of elements, and a Map deals with key-pair values.

我的直觉是您正试图在 List 和 Set 之间进行选择.

My gut feeling is that you're attempting to choose between a List and a Set.

如果你只想输入unique元素，或者更简洁地说，如果你只关心唯一值，那么某种Set是你最好的打赌 - 如果您不关心排序，可能是 HashSet.它提供 O(1) 时间基本操作，例如添加、删除、包含和大小.

If you wish to only enter unique elements, or to put it more succinctly, if you only care about unique values, then a Set of some kind is your best bet - probably HashSet if you don't care about ordering. It provides O(1) time for the basic operations, such as add, remove, contains, and size.

^{(有趣的是，HashSet 由 HashMap 支持，但提供了一个类似于 ArrayList 的接口.)}

^{(Interestingly enough, HashSet is backed by a HashMap, but provides an interface similar to ArrayList.)}

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