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Java TreeSet addAll() Method with Example

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

TreeSet Class addAll() method

  • addAll() method is available in java.util package.
  • addAll() method is used to copy all of the objects to this TreeSet and paste it in the given collection (co).
  • addAll() 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.
  • addAll() method may throw an exception at the time of copying all of the elements.
    • ClassCastException: This exception may throw when the given parameter is incompatible to compare.
    • NullPointerException: This exception may throw when the given parameter is null exists.


    public boolean addAll(Collection co);


  • Collection co – represents the collection object is to be added.

Return value:

The return type of the method is boolean, it returns true when we add all of the objects in the given collection (co) to this TreeSet otherwise it returns false.


// Java program to demonstrate the example 
// of boolean addAll(Collection co) method of TreeSet 

import java.util.*;

public class AddAllOfTreeSet {
    public static void main(String[] args) {
        // Instantiates a TreeSet object
        TreeSet < String > tree_set1 = new TreeSet < String > ();
        TreeSet < String > tree_set2 = new TreeSet < String > ();

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

        // Display TreeSet
        System.out.println("TreeSet1: " + tree_set1);
        System.out.println("TreeSet2: " + tree_set2);

        // By using addAll() method is to add
        // all of the elements exists in tree_set1 
        // into a tree_set2

        // Display Modified TreeSet2
        System.out.println("TreeSet2: " + tree_set2);


TreeSet1: [C, C++, JAVA, PHP, SFDC]
TreeSet2: []
TreeSet2: [C, C++, JAVA, PHP, SFDC]

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