sort a map on value

[liliya woland]

Hello, I got a map and would like to sort it based on the values. So far, I'm attempting to create a TreeSort and getting ClassCastException. Any ideas anyone how to sort a map?

List mapValues = new ArrayList(mapAllProducts.values());
List mapKeys = new ArrayList(mapAllProducts.keySet());
        TreeSet sortedSet = new TreeSet(mapAllProducts.values());

[Bear Bibeault]

Please take the time to choose the correct forum for your posts. This forum is for questions on Servlets.

This post has been moved to a more appropriate forum.

[Deva Sagar]

Take a look at the Collections class which has a bunch of utility methods for such operations on collections.

Collections.sort(mapValues) will sort the contents of mapValues

[Jim Yingst]

You can get all the values from a Map, put them in a List, and sort them using Collections.sort(). However this has no effect on the original Map Using a TreeMap won't help much either, as a TreeMap wants to sort by key, not value. You could solve this problem using two maps, where the second maps in reverse order (reversing key and value). Or you could use a TreeBidimap from Jakarta Commons Collections. That last is probably easiest.

[Garrett Rowe]

It looks like the values in your Map don't implement the Comparable interface. You could use the TreeSet Constructor that takes a Comparator object to do the sorting.

[liliya woland]

Unfortunately, I ended up using 2 maps. both maps have similar keys and different values. They get created in a loop simultaneously. Now, if I sort the first map, the second map will become useless. I think I'd have to use a different data structure for this.