is there a map that will supply me hashing in both direction?

I hold the followi开发者_开发技巧ng map

      Map<Integer, List<String>>

when I add a new string to a certain int I just add it to the list of that int value in my map.

Now, I also need to remove it from the last list it was located in.

I will elaborate for a second :

It is not the same instance of the string. I get an int and a String, I need to add it and remove it from the former List in the map that held the same string value.

This means that I need to hold another map of String to Integer ?

Do I need to maintain two collections?

thanks.

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It's kind of like a BiMap, but since your relationship is assymetrical (one int refers to a List of Strings whereas a String can only refer to one int), it's not going to be a perfect mtach.

It sounds to me as though you want two maps, the first being your Map<Integer, List<String>> and the second being a Map<String, Integer>. You'd want to encapsulate this in class, of course. Adding a new string is then:

1. If there's an entry for the String in Map<String, Integer>,
   • Get the Integer from that list.
   • Use it to look up the List from your Map<Integer, List<String>> and remove the String from it.
2. Add the String to the relevant List in your Map<Integer, List<String>>
3. Add an entry mapping the String to the Integer in the Map<String, Integer>.

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You could try using Guava's BiMap.