如何最好地比较 Java 中的两个集合并对其采取行动? [英] How Best to Compare Two Collections in Java and Act on Them?

问题描述

我有同一个对象的两个集合，CollectionoldSet 和 Collection新集.所需逻辑如下:

I have two collections of the same object, Collection<Foo> oldSet and Collection<Foo> newSet. The required logic is as follow:

• 如果 foo 在 (*) oldSet 但不是 newSet，则调用 doRemove(foo)
• else 如果 foo 不在 oldSet 中而是在 newSet 中，则调用 doAdd(foo)
• else 如果 foo 在两个集合中但被修改，则调用 doUpdate(oldFoo, newFoo)
• else if !foo.activated &&foo.startDate >= now，调用doStart(foo)
• else if foo.activated &&foo.endDate <= now，调用doEnd(foo)

• if foo is in(*) oldSet but not newSet, call doRemove(foo)
• else if foo is not in oldSet but in newSet, call doAdd(foo)
• else if foo is in both collections but modified, call doUpdate(oldFoo, newFoo)
• else if !foo.activated && foo.startDate >= now, call doStart(foo)
• else if foo.activated && foo.endDate <= now, call doEnd(foo)

(*) "in" 表示唯一标识符匹配，不一定是内容.

(*) "in" means the unique identifier matches, not necessarily the content.

当前(遗留)代码做了很多比较以找出removeSet、addSet、updateSet、startSet和 endSet，然后循环对每个项目进行操作.

The current (legacy) code does many comparisons to figure out removeSet, addSet, updateSet, startSet and endSet, and then loop to act on each item.

代码很乱(部分原因是我已经遗漏了一些意大利面条式的逻辑)，我正在尝试重构它.更多背景信息:

The code is quite messy (partly because I have left out some spaghetti logic already) and I am trying to refactor it. Some more background info:

• 据我所知，oldSet 和 newSet 实际上是由 ArrayList
支持的
• 每组包含少于 100 个项目，最有可能最多 20 个
• 此代码被频繁调用(以百万/天为单位)，尽管集合很少不同

我的问题:

• 如果我将 oldSet 和 newSet 转换为 HashMap(这里不关心顺序)，以 ID 作为键，它会使代码更易于阅读和比较吗?多少时间&内存性能是转换时的损失?
• 迭代这两个集合并执行适当的操作会更高效和简洁吗?

• If I convert oldSet and newSet into HashMap<Foo> (order is not of concern here), with the IDs as keys, would it made the code easier to read and easier to compare? How much of time & memory performance is loss on the conversion?
• Would iterating the two sets and perform the appropriate operation be more efficient and concise?

推荐答案

Apache 的 commons.collections 库有一个 CollectionUtils 类，该类提供了易于使用的集合操作/检查方法，例如交集、差集和并集.

Apache's commons.collections library has a CollectionUtils class that provides easy-to-use methods for Collection manipulation/checking, such as intersection, difference, and union.

org.apache.commons.collections.CollectionUtils API 文档是 此处.

The org.apache.commons.collections.CollectionUtils API docs are here.

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