Java – How to convert a Collection to List

apache-commons-collectioncollectionsjavalistsorting

I am using TreeBidiMap from the Apache Collections library. I want to sort this on the values which are doubles.

My method is to retrieve a Collection of the values using:

Collection coll = themap.values();

Which naturally works fine.

Main Question: I now want to know how I can convert/cast (not sure which is correct) coll into a List so it can be sorted?

I then intend to iterate over the sorted List object, which should be in order and get the appropriate keys from the TreeBidiMap (themap) using themap.getKey(iterator.next()) where the iterator will be over the list of doubles.

Best Solution

List list = new ArrayList(coll);
Collections.sort(list);

As Erel Segal Halevi says below, if coll is already a list, you can skip step one. But that would depend on the internals of TreeBidiMap.

List list;
if (coll instanceof List)
  list = (List)coll;
else
  list = new ArrayList(coll);