Create TreeSet in Java - How to add Elements to TreeSet

Published April 04, 2022

Creating a Java TreeSet first requires importing the java.util.TreeSet package therefore, you should import it first. Once this package has been imported, use the Syntax below to create your TreeSet:

TreeSet<Integer> TreeSet = new TreeSet<>();

 

The TreeSet is sorted in ascending order by default, but this can be customized using the Comparator interface.

The Common TreeSet Methods

• add(): the specified element is inserted into the set

• addAll(): Adds all elements of a collection to a set

• removeAll(): removes  all elements from the set

• remove(): removes specified element

• first(): gets the first element of the set

• last(): gets the last element of the set

 

Example of TreeSets

In this example, we create a TreeSets object and add elements with the add() and addAll() methods.

import java.util.TreeSet; public class TreeSetExample {     public static void main(String[] args) {         TreeSet<Integer> TS = new TreeSet<>();         //add elements using the add() method         TS.add(7);         TS.add(8);         TS.add(9);         System.out.println("First TreeSet: " + TS);         TreeSet<Integer> numbers = new TreeSet<>();         numbers.add(6);         // add element using the addAll() method         numbers.addAll(TS);         System.out.println("Second TreeSet: " + numbers);     } }

 

Output:

First TreeSet: [7, 8, 9]

Second TreeSet: [6, 7, 8, 9]