Bi-directional Map in Java

Question

I have a simple integer-to-string mapping in Java  but I need to be able to easily retrieve string from integer  and also integer from string  I ve tried Map  but it can retrieve only string from integer  it s one way   private static final Map lt Integer  String gt  myMap   new HashMap lt Integer  String gt        This works one way  String myString   myMap get myInteger       I would need something like  Integer myInteger   myMap getKey myString     Is there a right way to do it to have it both directions    Another problem is that I only have a few constant values that don t change  1- gt  low   2- gt  mid   3- gt  high   so it wouldn t be worth to go for a complicated solution

User · Answer

Creating a Guava BiMap and getting its inverted value is not so trivial.

A simple example:

import com.google.common.collect.BiMap;
import com.google.common.collect.HashBiMap;

public class BiMapTest {

  public static void main(String[] args) {

    BiMap<String, String> biMap = HashBiMap.create();

    biMap.put("k1", "v1");
    biMap.put("k2", "v2");

    System.out.println("k1 = " + biMap.get("k1"));
    System.out.println("v2 = " + biMap.inverse().get("v2"));
  }
}

User · Answer

There is no bidirectional map in the Java Standard API  Either you can maintain two maps yourself or use the BidiMap from Apache Collections

User · Answer

You can use the Google Collections API for that  recently renamed to Guava  specifically a BiMap  A bimap  or  quot bidirectional map quot   is a map that preserves the uniqueness of its values as well as that of its keys  This constraint enables bimaps to support an  quot inverse view quot   which is another bimap containing the same entries as this bimap but with reversed keys and values

User · Answer

Apache commons collections has a BidiMap

User · Answer

You could insert both the key value pair and its inverse into your map structure  but would have to convert the Integer to a string   map put  theKey    theValue    map put  theValue    theKey      Using map get  theValue   will then return  theKey    It s a quick and dirty way that I ve made constant maps  which will only work for a select few datasets    Contains only 1 to 1 pairs Set of values is disjoint from the set of keys  1- 2  2- 3 breaks it    If you want to keep  lt Integer  String gt  you could maintain a second  lt String  Integer gt  map to  put  the value -  key pairs

User · Answer

Use Google s BiMap It is more convenient

[java] Bi-directional Map in Java?

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