Set addAll() Method in Java (original) (raw)

Last Updated : 04 Feb, 2025

In Java, the **addAll() method of the Set class is used to add all the elements of a specified collection to the current collection. The elements are added randomly without following any specific order.

**Example 1: This example demonstrates how to **merge two **TreeSet **using the addAll() method.

Java `

// Java program to demonstrates // the working of addAll() import java.io.; import java.util.;

public class Geeks{ public static void main(String args[]) { // Creating an empty Set Set s1 = new TreeSet();

    // Use add() method to add 
    // elements into the Set 
    s1.add("A"); 
    s1.add("B"); 
    s1.add("C"); 
    
    // Displaying the Set 
    System.out.println("Initial Set: " + s1); 

    // Creating another Set 
    Set<String> s2 = new TreeSet<String>(); 

    // Use add() method to add 
    // elements into the Set 
    s2.add("D"); 
    s2.add("E"); 

    // Using addAll() method to Append 
    s1.addAll(s2); 

    // Displaying the final Set 
    System.out.println("Final Set: " + s1); 
} 

}

`

Output

Initial Set: [A, B, C] Final Set: [A, B, C, D, E]

Syntax of addAll() Method

boolean addAll(Collection<? extends E> c)

• **Parameter: The method takes a collection as an argument, which can be any subclass of theCollection interface.
• **Return Type: This method returns "true" if the element were added successfully, otherwise returns "false".

**Example 2: This example demonstrates how to **append elements from an **ArrayList **to a TreeSet using the addAll() method.

Java `

// Java Program to append elements from an ArrayList // to a TreeSet using the addAll() method import java.util.*;

public class Geeks { public static void main(String args[]) { // Creating an empty Set Set s1 = new TreeSet();

    // Use add() method to add elements into the Set
    s1.add("100");
    s1.add("200");
    s1.add("300");

    System.out.println("Initial Set: " + s1);

    // An array collection is created
    ArrayList<String> a = new ArrayList<String>();
    a.add("400");
    a.add("500");
    a.add("600");

    // Using addAll() method to Append
    s1.addAll(a);

    System.out.println("Final Set: " + s1);
}

}

`

Output

Initial Set: [100, 200, 300] Final Set: [100, 200, 300, 400, 500, 600]