How to sort a HashSet?

Question

For lists, we use the Collections.sort(List) method. What if we want to sort a HashSet?

Answer 1

You can wrap it in a TreeSet like this:

Set mySet = new HashSet();
mySet.add(4);
mySet.add(5);
mySet.add(3);
mySet.add(1);
System.out.println("mySet items "+ mySet);   

TreeSet treeSet = new TreeSet(mySet);   
System.out.println("treeSet items "+ treeSet);   

output :
mySet items [1, 3, 4, 5]
treeSet items [1, 3, 4, 5]

Set mySet = new HashSet();
mySet.add("five");
mySet.add("elf");
mySet.add("four");
mySet.add("six");
mySet.add("two");
System.out.println("mySet items "+ mySet);

TreeSet treeSet = new TreeSet(mySet);
System.out.println("treeSet items "+ treeSet);

output:
mySet items [six, four, five, two, elf]
treeSet items [elf, five, four, six, two]

requirement for this method is that the objects of the set/list should be comparable (implement the Comparable interface)