How to get a limited number of values from a HashMap or LinkedHashMap?

Question

Say I have a LinkedHashMap containing 216 entries, how would I get the first 100 values (here, of type Object) from a LinkedHashMap<Integer, Object>.

Answer 1

Ugly One-Liner

This ugly one-liner would do (and return a ArrayList<Object> in the question's case):

Collections.list(Collections.enumeration(lhMap.values())).subList(0, 100)

This would work for a HashMap as well, however HashMap being backed by a HashSet there's not guarantee that you will get the first 100 values that were entered; it would work on other types, with similar limitations.

Notes:

• relatively unefficient (read the Javadoc to know why - though there's worse!),
• careful when using views (read the Javadoc to know more),
• I did mention it was ugly.

Step-By-Step Usage Example

(as per the OP's comment)

Map<Integer, Pair<Double, SelectedRoad>> hashmap3 =
  new LinkedHashMap<Integer, Pair<Double, SelectedRoad>>();

// [...] add 216 elements to hasmap3 here somehow

ArrayList<Pair<Double,SelectedRoad>> firstPairs = 
  Collections.list(Collections.enumeration(hashmap3.values())).subList(0, 100)

// you can then view your Pairs' SelectedRow values with them with:
//  (assuming that:
//    - your Pair class comes from Apache Commons Lang 3.0
//    - your SelectedRoad class implements a decent toString() )
for (final Pair<Double, SelectedRoad> p : firstPairs) {
    System.out.println("double: " + p.left);
    System.out.println("road  : " + p.right);
}