Sorting a HashSet in Java Using Collections

Sorting a HashSet in Java

HashSet is a collection in Java that contains unique elements. Unlike a List or ArrayList, it does not support sorting natively. However, sorting a HashSet can be done by converting the data structure to an ArrayList and then using the Collections.sort() method. In this article, we'll discuss how to sort a HashSet using Java.

Using TreeSet to Sort a HashSet

The TreeSet interface extends the SortedSet interface and provides an implementation of a set that uses a tree for storage. This means that the elements in a TreeSet are sorted according to their natural ordering, or according to a Comparator provided at the time of creation of the set. This makes it very easy to sort a HashSet with the help of a TreeSet.

To sort a HashSet using a TreeSet, we can use the following code:

// Create an empty TreeSet 
TreeSet<String> sortedSet = new TreeSet<>(); 

// Copy all elements from HashSet to TreeSet 
sortedSet.addAll(hashSet); 

// Print the sorted TreeSet 
System.out.println("Sorted Set : " + sortedSet);

This above code will take the elements from the HashSet and add them to the TreeSet. The elements in the TreeSet will then be sorted according to their natural ordering.

Using ArrayList & Collections.sort() to Sort a HashSet

We can also use the ArrayList & Collections.sort() combination to sort a HashSet. To do this, we need to first convert the HashSet to an ArrayList and then use the Collections.sort() to sort the elements according to their natural ordering.

The following code shows how this can be done:

// Convert the HashSet to an ArrayList 
ArrayList<String> list = new ArrayList<>(hashSet); 

// Sort the ArrayList 
Collections.sort(list); 

// Print the sorted ArrayList 
System.out.println("Sorted List : " + list); 

This above code will take the HashSet and convert it to an ArrayList using the constructor of the ArrayList. Then, it will use the Collections.sort() method to sort the elements of the ArrayList according to their natural ordering.

Conclusion

In this article, we discussed two ways to sort a HashSet in Java - using a TreeSet and using the Collections.sort() method after converting the HashSet to an ArrayList. Both methods are relatively straightforward and easy to implement.