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Java TreeSet add() Method with Example

TreeSet Class add() method: Here, we are going to learn about the add() method of TreeSet Class with its syntax and example.
Submitted by Preeti Jain, on February 20, 2020

TreeSet Class add() method

  • add() method is available in java.util package.
  • add() method is used to add the given object(ob) to this TreeSet when it does not already exist otherwise it ignores it.
  • add() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
  • add() method may throw an exception at the time of adding an object.
    ClassCastException: This exception may throw when the given parameter is incompatible.


    public boolean add(Object ob);


  • Object ob – represents the object (ob) to be added in this TreeSet.

Return value:

The return type of the method is boolean, it returns true when the given object (ob) is to be added successfully otherwise it returns false when the given object is already exists in this TreeSet.


// Java program to demonstrate the example 
// of boolean add(Object ob) method of TreeSet 

import java.util.*;

public class AddOfTreeSet {
    public static void main(String[] args) {
        // Instantiates a TreeSet object
        TreeSet < String > tree_set = new TreeSet < String > ();

        // By using add() method is to add
        // the given object of this
        // TreeSet if not exists

        // Display TreeMap 
        System.out.println("TreeSet: " + tree_set);


TreeSet: [C, C++, JAVA, PHP, SFDC]

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