Question

oldUsers is just a subset of allUsers and all oldUsers are made in-active in the following list. The logic currently works, but I am iterating allUsers just to get the handle of oldUser every time, before I set the active flag to false. Is there a way to pull the appropriate record and make my modifications (oldUsers and allUsers is of type Set<User>)

for (User oldUser : oldUsers) {
    for (User  user : allUsers) {
        if (user.getId().equals(oldUser.getId())) {
            user.setActive(false);
        }
    }
}

Answer 1

If oldUsers contains copies or fresh instances of users, and you simply want to setActive(false) on those users in allUsers that have a matching id, then I suggest you override the .equals (and .hash) methods of User based on the user id. You could then do like this:

Set<User> toInactivate = new HashSet<User>(allUsers);
toInactivate.retainAll(oldUsers);
for (User u : toInactivate)
    u.setActive(false);

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Another way (perhaps even more elegant) would be to store the users in a Map<Integer, User> mapping user ids to users. You could then simply do

for (int id : oldUsers.keySet())
    allUsers.get(id).setActive(false);