在Java中检查另一个地图中的地图内容

Question

I need to write a small snippet of code where I need to check contents of a map (key value) if it exists in another map , remove it from the map

Eg

Map1:

1=>obj1
2=>obj21
3=>obj3 
4=>obj4

Other map Map2:

10=>obj10
20=>obj20
2=>obj2
30=>obj30
3=>obj3

The result of fun (Map1, Map2) after it executes it has the following ouput

Map2:

10=>obj10
2=>obj2
20=>obj20
30=>obj30 

Is iterating over the smaller map and checking contents (key, value) is iterating over the smaller map and checking the key and contents in the bigger map the most efficient way to go about it.

Answer 1

m1.entrySet().removeAll(m2.entrySet());

其中m1是要修改的地图，m2是需要从m1中删除的映射的地图。

Answer 2

private static <K, V> void fun(Map<K, V> a, Map<K, V> b) {
    Map<K, V> shortestMap = a.size() < b.size() ? a : b;
    Map<K, V> longestMap = a.size() > b.size() ? a : b;

    Set<Entry<K, V>> shortestMapEntries = shortestMap.entrySet();
    Set<Entry<K, V>> longestMapEntries = longestMap.entrySet();

    longestMapEntries.removeAll(shortestMapEntries);
}

Answer 3

private static <K, V> removeDuplicates(Map<K, V> map1, Map<K, V> map2) {
    for (K key : map1.keySet()) {
        V val1 = map1.get(key);
        V val2 = map2.get(key);
        if (val2 != null && val2.equals(val1)
            map2.remove(key);
    }
}

Answer 4

参见java.util.Collection

boolean removeAll(Collection<?> c)