Java比较两个地图 [英] Java compare two map

问题描述

在java中，我想比较两个地图，如下所示，我们是否有现有的API来执行此操作？

In java, I want to compare two maps, like below, do we have existing API to do this ?

谢谢

Map<String, String> beforeMap ;
beforeMap.put("a", "1");
beforeMap.put("b", "2");
beforeMap.put("c", "3");

Map<String, String> afterMap ;
afterMap.put("a", "1");
afterMap.put("c", "333");

//--- it should give me:
b is missing, c value changed from '3' to '333'

推荐答案

我使用Set的removeAll（）功能来设置键的差异以查找添加和删除。可以通过使用条目设置为HashMap来执行设置差异来检测实际更改.Entry使用键和值实现equals（）。

I'd use removeAll() functionality of Set to to do set differences of keys to find additions and deletions. Actual changes can be detected by doing a set difference using the entry set as HashMap.Entry implements equals() using both key and value.

Set<String> removedKeys = new HashSet<String>(beforeMap.keySet());
removedKeys.removeAll(afterMap.keySet());

Set<String> addedKeys = new HashSet<String>(afterMap.keySet());
addedKeys.removeAll(beforeMap.keySet());

Set<Entry<String, String>> changedEntries = new HashSet<Entry<String, String>>(
        afterMap.entrySet());
changedEntries.removeAll(beforeMap.entrySet());

System.out.println("added " + addedKeys);
System.out.println("removed " + removedKeys);
System.out.println("changed " + changedEntries);

输出

added []
removed [b]
changed [c=333]

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