How to convert a Collection to List?

Question

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

Answer 1

Something like this should work, calling the ArrayList constructor that takes a Collection:

List theList = new ArrayList(coll);

Answer 2

I think Paul Tomblin's answer may be wasteful in case coll is already a list, because it will create a new list and copy all elements. If coll contains many elemeents, this may take a long time.

My suggestion is:

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

Answer 3

Java 10 introduced List#copyOf which returns unmodifiable List while preserving the order:

List<Integer> list = List.copyOf(coll);

Answer 4

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);

Answer 5

I believe you can write it as such:

coll.stream().collect(Collectors.toList())

Answer 6

Use streams:

someCollection.stream().collect(Collectors.toList())