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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.

Syntax:

    public boolean addAll(Collection co);

Parameter(s):

• 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.

Example:

// 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
        tree_set1.add("C");
        tree_set1.add("C++");
        tree_set1.add("JAVA");
        tree_set1.add("PHP");
        tree_set1.add("SFDC");

        // 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
        tree_set2.addAll(tree_set1);

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

Output

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