Is there a better way to implement search map?

Question

I have a map of objects Members

public class Member {

int id;
String firstName;
String lastName;
String street;
String city;
...

with id as a key, which is doing job for me and I don't want to change structure of the map.

I need to implement search by name functionality. So far I can think only about 2 solutions:

1st is to iterate trough the map - not most time efficient way

2nd is to create another map with member's names as a keys and ids as values as reference to my main map and search trough this map to find the key - efficient with time but less in space, which not worry me too much

I want to ask if there is more efficient (better) way to implement search of map in my case?

Answer 1

You're right that iterating through the map is not the most efficient way; that will be O(n) with n Members .

You're on the right track with creating a second Map keyed by the members' names. What I would change is have the Member references as the values for this second map too, so that you don't have to retrieve the ID then perform a second lookup on the first map to retrieve the Member . This would be a Map<String, Member> .

Answer 2

There's no point in creating a second Map if it would require 2 lookups (first find the id for a given name and then find the Member of that id).

It would be more efficient if the second Map would map the name keys to the Member values (ie Map<String,Member> ). You might be thinking that such an approach would require more memory compared to a Map<String,Integer> , but you would be wrong. A reference to a Member instance takes the same amount of memory as a reference to an Integer instance. Just because you have two Map s that contain the same values, doesn't mean that the Member instances need to be duplicated. Only the references to those isntance would be duplicated.