Shortcut for adding to List in a HashMap
- by Damo
I often have a need to take a list of objects and group them into a Map based on a value contained in the object. Eg. take a list of Users and group by Country.
My code for this usually looks like:
Map<String, List<User>> usersByCountry = new HashMap<String, List<User>>();
for(User user : listOfUsers) {
if(usersByCountry.containsKey(user.getCountry())) {
//Add to existing list
usersByCountry.get(user.getCountry()).add(user);
} else {
//Create new list
List<User> users = new ArrayList<User>(1);
users.add(user);
usersByCountry.put(user.getCountry(), users);
}
}
However I can't help thinking that this is awkward and some guru has a better approach. The closest I can see so far is the MultiMap from Google Collections.
Are there any standard approaches?
Thanks!
