Java 双向映射
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Bidirectional Map
提问by mawia
Can you suggest a kind of map or similar data structure where we can get both the value and key from each other at equal ease. That is to say, that each may be used to find other.
你能建议一种地图或类似的数据结构，我们可以同样轻松地从彼此那里获取值和键。也就是说，每个都可以用来找到另一个。
回答by Joni
The most common solution is using two maps. You can easily encapsulate them in a class with a friendly interface by extending AbstractMap. (Update:This is how Guava's HashBiMapis implemented: two maps)
最常见的解决方案是使用两个地图。您可以通过扩展AbstractMap. （更新：这是 Guava 的HashBiMap实现方式：两张地图）
Creating a new data structure using nothing but arrays and custom classes has few advantages. The map implementations are lightweight wrappers of a data structure that indexes the keys. Since you need two indexes you might as well use two complete maps.
仅使用数组和自定义类创建新的数据结构几乎没有优势。映射实现是索引键的数据结构的轻量级包装器。由于您需要两个索引，您不妨使用两个完整的地图。
回答by Jesper
Java doesn't have a bidirectional map in its standard library.
Java 在其标准库中没有双向映射。
Use for example BiMap<K, V>from Google Guava.
使用例如BiMap<K, V>来自Google Guava。
回答by Buhake Sindi
Google Guavacontains a BiMap(BiDirectional Map).
Google Guava包含一个BiMap(BiDirectional Map)。
回答by kervin
回答by Javanator
If you feel it pain importing some third party library. How about this simple class.
如果你觉得导入一些第三方库很痛苦。这个简单的类怎么样。
public class BiMap<K,V> {
HashMap<K,V> map = new HashMap<K, V>();
HashMap<V,K> inversedMap = new HashMap<V, K>();
void put(K k, V v) {
map.put(k, v);
inversedMap.put(v, k);
}
V get(K k) {
return map.get(k);
}
K getKey(V v) {
return inversedMap.get(v);
}
}
Make sure K and V class has proper hashCode implementation.
确保 K 和 V 类具有正确的 hashCode 实现。
回答by Gregor
well for the average usecase where you need a Dictionary like that, I see nothing wrong with a KISS solution, just put'ting the key and value vice versa, saving the overhead of a second Map or even library only for that purpose:
对于需要这样的字典的一般用例，我认为 KISS 解决方案没有任何问题，只需将键和值放在相反的位置，仅为此目的节省第二个 Map 甚至库的开销：
myMap.put("apple", "Apfel");
myMap.put("Apfel", "apple");
回答by Narsi Reddy Nallamilli
You can define an enum and define helper method to get key. Performance is way too far better compared to BidiMap. E.g
您可以定义一个枚举并定义辅助方法来获取密钥。与 BidiMap 相比，性能要好得多。例如
public enum Fruit {
APPLE("_apple");
private final String value;
Fruit(String value){
this.value=value;
}
public String getValue(){
return this.value;
}
public static String getKey(String value){
Fruit fruits[] = Fruit.values();
for(Fruit fruit : fruits){
if(value.equals(fruit.value)){
return fruit.name();
}
}
return null; }
}
回答by Davut Gürbüz
Based on this answerin this QA and its comments I wrote following. [Will be tested]
基于此 QA 中的这个答案及其评论，我写了以下内容。[将被测试]
Bidirectional Map
双向映射
import java.util.HashMap;
public class BidirectionalMap<K, V> extends HashMap<K, V> {
private static final long serialVersionUID = 1L;
public HashMap<V, K> inversedMap = new HashMap<V, K>();
public K getKey(V value) {
return inversedMap.get(value);
}
@Override
public int size() {
return this.size();
}
@Override
public boolean isEmpty() {
return this.size() > 0;
}
@Override
public V remove(Object key) {
V val=super.remove(key);
inversedMap.remove(val);
return val;
}
@Override
public V get(Object key) {
return super.get(key);
}
@Override
public V put(K key, V value) {
inversedMap.put(value, key);
return super.put(key, value);
}
}
