How do I sort a set in Java?

Question

In Java, I have a set, and I want to turn it into a sorted list. Is there a method in the collections package that will do this for me?

Answer 1

There's no single method to do that. Use this:

@SuppressWarnings("unchecked")
public static <T extends Comparable> List<T> asSortedList(Collection<T> collection) {
  T[] array = collection.toArray(
    (T[])new Comparable[collection.size()]);
  Arrays.sort(array);
  return Arrays.asList(array);
}

Answer 2

sorted set:
return new TreeSet(setIWantSorted)

Answer 3

...you answered your own question 38 seconds after you had asked it?

List myList = new ArrayList(collection); Collections.sort(myList); should do the trick however. Add flavour with Generics where applicable.

Answer 4

The answer provided by the OP is not the best. It is inefficient, as it creates a new List and an unnecessary new array. Also, it raises "unchecked" warnings because of the type safety issues around generic arrays.

Instead, use something like this:

public static
<T extends Comparable<? super T>> List<T> asSortedList(Collection<T> c) {
  List<T> list = new ArrayList<T>(c);
  java.util.Collections.sort(list);
  return list;
}

Answer 5

You can convert a set into a ArrayList. where you can sort ArrayList using Collections.sort(List);

here is the code..

    keySet = (Set) map.keySet();

    System.out.println("key Set  -----------------------> " + keySet);

    ArrayList list = new ArrayList(keySet);

    System.out.println("List ----------------------> "+ list);

    Collections.sort(list);