以有效的方式从Map中删除多个键？

I have a Map<String,String> with large number of key values pairs. Now I want to remove selected keys from that Map. Following code shows what I did to achieve that.

我有一个Map ，包含大量的键值对。现在我想从该Map中删除选定的键。以下代码显示了我为实现这一点所做的工作。，string>

Set keySet = new HashSet(); //I added keys to keySet which I want to remove.

Then :

然后：

Iterator entriesIterator = keySet.iterator();
while (entriesIterator.hasNext()) {
   map.remove( entriesIterator.next().toString());
}

This is working. I just want to know, what would be a better way to achieve my requirement ?

这很有效。我只想知道，实现我的要求会有什么更好的方法？

2 个解决方案

#1

172

Assuming your set contains the strings you want to remove, you can use the keySet method and map.keySet().removeAll(keySet);.

假设您的set包含要删除的字符串，可以使用keySet方法和map.keySet（）。removeAll（keySet）;.

keySet returns a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa.

keySet返回此映射中包含的键的Set视图。该集由地图支持，因此对地图的更改将反映在集中，反之亦然。

Contrived example:

举例：

Map<String, String> map = new HashMap<>();
map.put("a", "");
map.put("b", "");
map.put("c", "");

Set<String> set = new HashSet<> ();
set.add("a");
set.add("b");

map.keySet().removeAll(set);

System.out.println(map); //only contains "c"

#2

Just for the sake of completeness:

只是为了完整起见：

As guessed java.util.AbstractSet#removeAll really iterates over all entries, but with one little trick: It uses the iterator of the smaller collection:

正如猜测java.util.AbstractSet＃removeAll真的遍历所有条目，但有一个小技巧：它使用较小集合的迭代器：

if (size() <= collection.size()) {
    Iterator<?> it = iterator();
    while (it.hasNext()) {
        if (collection.contains(it.next())) {
            it.remove();
        }
    }
} else {
    Iterator<?> it = collection.iterator();
    while (it.hasNext()) {
        remove(it.next());
    }
}

#1

172