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

Add all your objects to the TreeSet, you will get a sorted Set. Below is a raw example.

HashSet myHashSet = new HashSet();
myHashSet.add(1);
myHashSet.add(23);
myHashSet.add(45);
myHashSet.add(12);

TreeSet myTreeSet = new TreeSet();
myTreeSet.addAll(myHashSet);
System.out.println(myTreeSet); // Prints [1, 12, 23, 45]

Answer 2

SortedSet has been added Since java 7 https://docs.oracle.com/javase/8/docs/api/java/util/SortedSet.html

Answer 3

You can use a TreeSet instead.

Answer 4

We can not decide that the elements of a HashSet would be sorted automatically. But we can sort them by converting into TreeSet or any List like ArrayList or LinkedList etc.

// Create a TreeSet object of class E
TreeSet<E> ts = new TreeSet<E> ();

// Convert your HashSet into TreeSet
ts.addAll(yourHashSet);

System.out.println(ts.toString() + "\t Sorted Automatically");

Answer 5

You can use Java 8 collectors and TreeSet

list.stream().collect(Collectors.toCollection(TreeSet::new))

Answer 6

Just in-case you don't wanna use a TreeSet you could try this.

set = set.stream().sorted().collect(Collectors.toCollection(LinkedHashSet::new));