Java比较两个地图

Question

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？

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'

Answer 1

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

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);

产量

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

Answer 2

Guava Maps类有一些方法来计算一对映射之间的差异.但是,这些方法为您提供了一个表示差异的数据结构,而不是一个漂亮的打印字符串.