List vs Map in Java

Question

I didnt get the sense of Maps in Java. When is it recommended to use a Map instead of a List?

thanks in advance,

nohereman

Answer 1

I thinks its a lot the question of how you want to access your data. With a map you can "directly" access your items with a known key, in a list you would have to search for it, evan if its sorted.

Compare:

List list = new ArrayList();
//Fill up the list
// Want to get object "peter"
for( MyObject m : list ) {
 if( "peter".equals( m.getName() ) {
    // found it
 }
}

In a map you can just type

Map map = new HashMap();
// Fill map
MyObject getIt = map.get("peter");

If you have data to process and need to do it with all objects anyway, a list is what you want. If you want to process single objects with well known key, a map is better. Its not the full answer (just my 2...) but I hope it might help you.