Convert HashSet to TreeSet in Java [3 ways]

In this tutorial, we will be learning how to convert HashSet to TreeSet in Java. In the last tutorial we have seen how to convert HashSet to an Array in Java. There are 3 ways to achieve our goal of converting HashSet to TreeSet in Java:

1. Using TreeSet constructor [Easiest]

2. Using addAll() method

3. Using for-each

Read Also: Difference between HashSet and TreeSet in Java

Let's dive deep into the topic:

Convert HashSet to TreeSet in Java

1. Using TreeSet constructor

The easiest way to convert HashSet to TreeSet is by using TreeSet constructor as shown below in the example:

 import java.util.*;

public class HashSetToTreeSet {
    public static void main(String args[]) {
      
      // Creating a HashSet object
      HashSet<String> hashset = new HashSet<String>();
      
      // Putting elements to HashSet object
      hashset.add("Air");
      hashset.add("Water");
      hashset.add("Fire");
      
      // Printing HashSet elements 
      System.out.println("HashSet elements are: "+ hashset);
      
      // Converting HashSet to TreeSet using TreeSet constructor
      TreeSet<String> treeset = new TreeSet<>(hashset);
      
      // Iterating over the TreeSet elements
      for (String element : treeset)
      {
          System.out.println("TreeSet elements are: "+ element);
      }
    }
}

Output:

HashSet elements are: [Water, Fire, Air]
TreeSet elements are: Air
TreeSet elements are: Fire
TreeSet elements are: Water

2. Using addAll() method

Another way to convert HashSet to TreeSet in Java is by using addAll() method as shown below in the example:

 import java.util.*;

public class HashSetToTreeSet2 {
    public static void main(String args[]) {
      
      // Create a HashSet object
      HashSet<String> hashset2 = new HashSet<String>();
      
      // Adding elements to HashSet object
      hashset2.add("Books");
      hashset2.add("Bag");
      hashset2.add("Bottle");
      
      // Displaying HashSet elements 
      System.out.println("Printing HashSet elements: "+ hashset2);
      
      // Creating TreeSet object
      TreeSet<String> treeset2 = new TreeSet<>();
      
      // Converting HashSet to TreeSet using addAll() method
      treeset2.addAll(hashset2);
      
      // Iterating and printing the TreeSet elements
      for (String str : treeset2)
      {
         System.out.println("TreeSet element is: "+ str);
      }
    }
}

Output:

Printing HashSet elements: [Bottle, Bag, Books]
TreeSet element is: Bag
TreeSet element is: Books
TreeSet element is: Bottle

3. Using for-each

We can also convert HashSet to TreeSet using for-each loop as shown below in the example:

 import java.util.*;

public class HashSetToTreeSet3 {
    public static void main(String args[]) {
      
      // Initializing HashSet object
      HashSet<String> hashset3 = new HashSet<String>();
      
      // Put elements to HashSet object
      hashset3.add("Washing Machine");
      hashset3.add("Television");
      hashset3.add("Refrigerator");
      
      // Showing HashSet elements 
      System.out.println("Showing HashSet elements: "+ hashset3);
      
      // Producing TreeSet object
      TreeSet<String> treeset3 = new TreeSet<>();
      
      // Converting HashSet to TreeSet using for-each
      for (String str : hashset3)
      {
        treeset3.add(str);  
      }
      System.out.println("TreeSet elements are: "+ treeset3);      
    }
}

Output:

Showing HashSet elements: [Television, Refrigerator, Washing Machine]
TreeSet elements are: [Refrigerator, Television, Washing Machine]

That's all for today. Please mention in the comments if you have any questions related to how to convert HashSet to TreeSet in Java.