How do I add multiple values to the same key in a TreeMap?

Question

My tree Map is

Map<String, Double> restrMap = new TreeMap<String, Double>();

While adding the below two value to the treeMap, it only shows one. The second value, when comes updates the first one.

6, 8.00
6, 5.00

How can I add two values for the same key, perhaps in different rows?

A map is not a table. Its purpose is to find a value by a key. So there is only one value for a key. You can make that value a container of several objects. — RealSkeptic, Mar 26 '15 at 20:20

score 5 · Answer 1 · answered Mar 26 '15 at 20:18

5

If you are adding multiple values to the same key, consider having a Map of Lists.

Map<String, List<Double>> restrMap = new TreeMap<String, List<Double>>();

answered Mar 26 '15 at 20:18

Marc

score 2 · Answer 2 · answered Mar 26 '15 at 20:19

2

A map has only one value associated to a specific key.

If you want several values, you can:

use Guava's Multimap
use Apache Commons Collections MultiMap
use a Map<Key, Set<Value>> or any other collection for the values that would meet your needs

answered Mar 26 '15 at 20:19

Jean Logeart

score 2 · Answer 3 · answered Mar 26 '15 at 20:23

2

Java does not have multimap, but you could uses another container in the map value.

Map<String, List<Double>> restrMap = new TreeMap<String, List<Double>>();

answered Mar 26 '15 at 20:23

BK Batchelor

3 Answers3