Set addAll() Method in Java
Last Updated :
04 Feb, 2025
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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 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<String> s1 = new TreeSet<String>();
// 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 the Collection 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 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<String> s1 = new TreeSet<String>();
// 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]
