Java ArrayList set() Method

Last Updated : 25 Jul, 2026

The set() method of the ArrayList class replaces the element at a specified index with a new element. Unlike add(), it does not change the size of the list; instead, it updates the existing element and returns the element that was previously stored at that position.

Java 
import java.util.ArrayList;

public class GFG {
    public static void main(String[] args) {
      
        // Create an ArrayList and 
        // add elements
        ArrayList<Integer> n = new ArrayList<>();
        n.add(1);
        n.add(2);
        n.add(3);
        n.add(4);
        n.add(5);

        // Print the original ArrayList
        System.out.println("Before operation: " + n);

        // Replace element at 
        // index 3 with 9
        int r = n.set(3, 9);

        System.out.println("After operation: " + n);
        System.out.println("Replaced element: " + r);
    }
}

Output
Before operation: [1, 2, 3, 4, 5]
After operation: [1, 2, 3, 9, 5]
Replaced element: 4

Explanation: In this example, the set() method replaces the element at index 3 (4) with 9. The method returns the old element (4), while the ArrayList is updated to [1, 2, 3, 9, 5].

Syntax

public E set(int index, E element)

Parameters:

  • index: Index of the element to replace.
  • element: Element to be stored at the specified position.

Returns Value: It returns the element that was previously at the specified position.

Exception: IndexOutOfBoundsException: Thrown if the index is out of the valid range (index < 0 or index >= size).

Example: Handling an Invalid Index

Java 
// Handling IndexOutOfBoundsException
import java.util.ArrayList;

public class GFG {
    public static void main(String[] args) {
        try {
          
            // Create an ArrayList and add elements
            ArrayList<Integer> n = new ArrayList<>();
            n.add(1);
            n.add(2);
            n.add(3);
            n.add(4);
            n.add(5);

            // Print the original ArrayList
            System.out.println("Before operation: " + n);

            // Attempt to replace an element at an invalid index
            n.set(7, 9);
        } catch (IndexOutOfBoundsException e) {
          
            // Handle the exception
            System.out.println("Exception: " + e);
        }
    }
}

Output
Before operation: [1, 2, 3, 4, 5]
Exception: java.lang.IndexOutOfBoundsException: Index 7 out of bounds for length 5

Explanation: In this example, the set() method attempts to replace an element at index 7, which is outside the valid range of the ArrayList. As a result, an IndexOutOfBoundsException is thrown and handled using a try-catch block.

Example: Updating a Student Name

Java 
import java.util.ArrayList;

public class GFG {
    public static void main(String[] args) {

        ArrayList<String> students = new ArrayList<>();

        students.add("Amit");
        students.add("Rahul");
        students.add("Priya");

        students.set(1, "Rohan");

        System.out.println(students);
    }
}

Output
[Amit, Rohan, Priya]

Explanation: The element "Rahul" at index 1 is replaced with "Rohan". The size of the ArrayList remains unchanged.

set() Vs add()

set()add()
Replaces an existing element.Inserts a new element.
Does not change the size of the list.Increases the size of the list.
Requires an existing valid index.Can append an element or insert at a valid index.
Returns the replaced element.Returns boolean (or void for add(int, E)).

Advantages of set() Method

  • Updates an existing element without changing the list size.
  • Provides direct access to elements using their index.
  • Returns the replaced element, making it easy to track updates.
  • Executes in constant time for ArrayList.
  • Simplifies element replacement without removing and adding elements manually.
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