TreeSet addAll() Method in Java

The java.util.TreeSet.addAll(Collection C) method is used to append all of the elements from the mentioned collection to the existing set. The elements are added randomly without following any specific order. 

Syntax:

boolean addAll(Collection C)

Parameters: The parameter C is a collection of any type that is to be added to the tree set. 

Return Value: The method returns true if it successfully appends the elements of the collection C to the TreeSet otherwise it returns False. 

Below programs illustrate the Java.util.TreeSet.addAll() method: 

Program 1 : Appending a tree set. 

Java

// Java code to illustrate addAll()
import java.io.*;
import java.util.TreeSet;

public class TreeSetDemo {
    public static void main(String args[])
    {
        // Creating an empty TreeSet
        TreeSet<String> tree = new TreeSet<String>();

        // Use add() method to add elements into the Set
        tree.add("Welcome");
        tree.add("To");
        tree.add("Geeks");
        tree.add("4");
        tree.add("Geeks");
        tree.add("TreeSet");

        // Displaying the TreeSet
        System.out.println("TreeSet: " + tree);

        // Creating anothe TreeSet
        TreeSet<String> tree_two = new TreeSet<String>();

        // Use add() method to add elements into the Set
        tree_two.add("Hello");
        tree_two.add("World");

        // Using addAll() method to Append
        tree.addAll(tree_two);

        // Displaying the final tree
        System.out.println("TreeSet: " + tree);
    }
}

Output:

TreeSet: [4, Geeks, To, TreeSet, Welcome]
TreeSet: [4, Geeks, Hello, To, TreeSet, Welcome, World]

Program 2 : Appending an ArrayList. 

Java

// Java code to illustrate addAll()
import java.io.*;
import java.util.TreeSet;
import java.util.ArrayList;

public class TreeSetDemo {
    public static void main(String args[])
    {
        // Creating an empty TreeSet
        TreeSet<String> tree = new TreeSet<String>();

        // Use add() method to add elements into the Set
        tree.add("Welcome");
        tree.add("To");
        tree.add("Geeks");
        tree.add("4");
        tree.add("Geeks");
        tree.add("TreeSet");

        // Displaying the TreeSet
        System.out.println("TreeSet: " + tree);

        // An array collection is created
        ArrayList<String> collect = new ArrayList<String>();
        collect.add("A");
        collect.add("Computer");
        collect.add("Portal");

        // Using addAll() method to Append
        tree.addAll(collect);

        // Displaying the final tree
        System.out.println("Final TreeSet: " + tree);
    }
}

Output:

TreeSet: [4, Geeks, To, TreeSet, Welcome]
Final TreeSet: [4, A, Computer, Geeks, Portal, To, TreeSet, Welcome]