How to Merge Two TreeSets into One while Preserving Natural Order?

In Java, TreeSet is a pre-defined class that implements the Set interface, and it provides a sorted set of elements with no duplicates. This uses a Red-Black Tree data structure for storage. It is a part of the java.util package.

Key Terminologies:

• Set: A set can be defined as a collection that contains unique elements. The Set interface can be implemented in the TreeSet class.
• Comparator: The comparator is a pre-defined interface, and it is used to define the custom ordering for objects it can be provided custom ordering with specified rules by the comparator.

Syntax of Creating a TreeSet:

TreeSet<Type> treeSet = new TreeSet<>();

Step-by-Step Implementation:

• Create the class named GfGMergeTreeSets and write the main method into the class.
• Now, create the two tree sets and add the elements into the tree sets.
• Create one more TreeSet with one TreeSet element, then add another tree element into it.
• Print the resultant tree set.

Below is the Program to Merge Two TreeSets into One while Preserving Natural Order:

// Java program to merge two TreeSets
// Into one while preserving natural order
import java.util.TreeSet;

// Driver Class
public class GfGMergeTreeSets 
{
      // Main Function
    public static void main(String args[]) 
    {
        // Create two TreeSets
        TreeSet<Integer> set1 = new TreeSet<>();
           
          // Adding the elements into the set1
        set1.add(5);
        set1.add(25);
        set1.add(15);

        TreeSet<Integer> set2 = new TreeSet<>();
        
          // Adding the elements into the set1
        set2.add(3);
        set2.add(8);
        set2.add(12);

        // Merge the two TreeSets
        TreeSet<Integer> mergedSet = new TreeSet<>(set1);
        mergedSet.addAll(set2);

        System.out.println("Merged TreeSet: " + mergedSet);
    }
}

Merged TreeSet: [3, 5, 8, 12, 15, 25]

Explanation of the above Program:

• The above Java program is the example of merging two tree sets into one while preserving natural order.
• We have created two tree sets and added the elements to the two tree sets.
• After that, we have created one more tree set with the set1 element and added the set2 using the addAll() method.
• A last, all elements are merged and stored in the sorted order of the tree set.