Java ArrayList set() Method (original) (raw)

Last Updated : 12 Dec, 2024

The **set() method of the ArrayList class in Java is used to replace an element at a specified position with a new value. This is very useful when we need to update an existing element in an ArrayList while maintaining the list’s structure.

**Example 1: Here, we will use the **set() method to update an element in an ArrayList.

Java `

// Update an element in an ArrayList 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 the above example, it replaced an element in an ArrayList and prints both the updated list and the replaced element.

Syntax of ArrayList set() Method

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 2: Here, this example will show how **trying to replace an element at an invalid index results in an exception.

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