Java中的反向HashMap键和值 [英] Reverse HashMap keys and values in Java
问题描述
这是一个简单的问题,我有一个简单的 HashMap,我想反转它的键和值.
It's a simple question, I have a simple HashMap of which i want to reverse the keys and values.
HashMap<Character, String> myHashMap = new HashMap<Character, String>();
myHashMap.put('a', "test one");
myHashMap.put('b', "test two");
我想创建一个新的 HashMap,在其中放置对立面.
and I want to create a new HashMap in which i put the opposites.
HashMap<String, Character> reversedHashMap = new HashMap<String, Character>();
e.g. Keys "test one" & "test two" and values 'a' & 'b'.
推荐答案
它们都是独一无二的,是的
They all are unique, yes
如果您确定您的值是唯一的,您可以遍历旧地图的条目.
If you're sure that your values are unique you can iterate over the entries of your old map .
Map<String, Character> myNewHashMap = new HashMap<>();
for(Map.Entry<Character, String> entry : myHashMap.entrySet()){
myNewHashMap.put(entry.getValue(), entry.getKey());
}
或者,您可以使用双向地图,例如 Guava 提供和使用 inverse()
方法:
Alternatively, you can use a Bi-Directional map like Guava provides and use the inverse()
method :
BiMap<Character, String> myBiMap = HashBiMap.create();
myBiMap.put('a', "test one");
myBiMap.put('b', "test two");
BiMap<String, Character> myBiMapInversed = myBiMap.inverse();
作为 java-8出来了,你也可以这样:
As java-8 is out, you can also do it this way :
Map<String, Integer> map = new HashMap<>();
map.put("a",1);
map.put("b",2);
Map<Integer, String> mapInversed =
map.entrySet()
.stream()
.collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey))
最后,我将我的贡献添加到 质子包库,其中包含 Stream API 的实用方法.有了它,你可以这样做:
Finally, I added my contribution to the proton pack library, which contains utility methods for the Stream API. With that you could do it like this:
Map<Character, String> mapInversed = MapStream.of(map).inverseMapping().collect();
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