java - How to convert Map<String, String> to Map<Long, String> ? (option : using guava)

Question

I have a Map<String, String> the String key is nothing but numeric value like "123" etc. I'm getting numeric value because this values are coming from the UI in my JSF component. I don't want to change the contract of UI component.

Now I would like to create a Map<Long, String> based on the above Map, I saw some transform methods in the Maps class but all are focusing on the converting value and not key.

Is there any better way to convert Map<String, String> to Map<Long, String> ?

Answer 1

@Vivin's answer is correct, but I think it's useful to explain why Guava doesn't have any method to allow you to transform the keys of a Map (or to transform a Set at all).

All of Guava's methods for transforming and filtering produce lazy results... the function/predicate is only applied when needed as the object is used. They don't create copies. Because of that, though, a transformation can easily break the requirements of a Set.

Let's say, for example, you have a Map<String, String> that contains both "1" and "01" as keys. They are both distinct Strings, and so the Map can legally contain both as keys. If you transform them using Long.valueOf(String), though, they both map to the value 1. They are no longer distinct keys. This isn't going to break anything if you create a copy of the map and add the entries, because any duplicate keys will overwrite the previous entry for that key. A lazily transformed Map, though, would have no way of enforcing unique keys and would therefore break the contract of a Map.