比较两张几乎相同的地图，找出不同的关键值

Question

所以我有两个相同的映射，字符串作为键，整数作为值，我知道在某些事件之后，map2中只有1个值递增1。

Map<String, Integer> map1 = new HashMap<>();
map1.put("First", 1)
map1.put("Second", 2)
map1.put("Third", 3)
Map<String, Integer> map2 = new HashMap<>();
map2.put("First", 1)
map2.put("Second", 3)
map2.put("Third", 3)

所以我的问题是如何返回“第二”键，因为它的值增加了1。

Answer 1

似乎您只想获取键，而不想获取值，所以下面的方法正好可以做到这一点。

public static <K> List mapDifference(Map<? extends K, ? extends Object> map1, Map<? extends K, ? extends Object> map2)
{
        List<K> keys = new ArrayList<K>();
        Set<Map.Entry<? extends K, ? extends Object>> set;
        Map<? extends K, ? extends Object> other;
        if(map1.size() > map2.size()) {
            set = map1.entrySet(); other = map2;
        } else {
            set = map2.entrySet(); other = map1;
        }
        Iterator<Map.Entry<? extends K, ? extends Object>> iterator = set.iterator();
        while(iterator.hasNext()) {
            Map.Entry<? extends K, ?  extends Object> entry = iterator.next();
            K key = entry.getKey();
            if(!other.containsKey(key) || !other.get(key).equals(entry.getValue())) {
                keys.add(key);
            }
        }
        return keys;
}

测试

Map<String, Integer> map1 = new HashMap<>();
map1.put("First", 1);
map1.put("Second", 2);
map1.put("Third", 3);
Map<String, Integer> map2 = new HashMap<>();
map2.put("First", 1);
map2.put("Second", 3);
map2.put("Third", 3);

List<String> diff = mapDifference(map1, map2);
System.out.println(diff);

[Second]

Map<String, Integer> map1 = new HashMap<>();
map1.put("First", 1);
map1.put("Second", 2);
map1.put("Third", 3);
Map<String, Integer> map2 = new HashMap<>();
map2.put("First", 1);
map2.put("Second", 3);
map2.put("Third", 3);
map2.put("Forth", 4);

List<String> diff = mapDifference(map1, map2);
System.out.println(diff);

[Second, Forth]