How to Replace a Element in Java ArrayList?

To replace an element in Java ArrayList, set() method of java.util. An ArrayList class can be used. The set() method takes two parameters the indexes of the element that has to be replaced and the new element. The index of an ArrayList is zero-based. So, to replace the first element, 0 should be the index passed as a parameter.

Declaration:

public Object set(int index, Object element)

Return Value: The element that is at the specified index

Exception Throws: IndexOutOfBoundsException
This occurs when the index is out of range.

index < 0 or index >= size()

Implementation:

Here we will be proposing out 2 examples wherein one of them we will be setting the index within bound and in the other, we will be setting the index out of bounds. 

Example 1: Where Index is Within Bound 

Java

// Java program to demonstrate set() Method of ArrayList
// Where Index is Within Bound 

// Importing required classes
import java.io.*;
import java.util.*;

// Main class
class GFG {

  // Main driver method
  public static void main(String[] args) {

    // Try block to check for exceptions
    try {

      // Creating an object of Arraylist class
      ArrayList<String> list = new ArrayList<>();


      // Adding elements to the List
      // using add() method

      // Custom input elements
      list.add("A");
      list.add("B");
      list.add("C");
      list.add("D");

      // Print all the elements added in the above object
      System.out.println(list);

      // 2 is the index of the element "C".
      //"C" will be replaced by "E"
      list.set(2, "E");

      // Printing the newly updated List
      System.out.println(list);

    }

    // Catch block to handle the exceptions
    catch (Exception e) {

      // Display the exception on the console
      System.out.println(e);
    }
  }
}

Output

[A, B, C, D]
[A, B, E, D]

Example 2: Where Index is Out of Bound

Java

// Java program to demonstrate set() Method of ArrayList 
// Where Index is Out of Bound

// Importing required classes
import java.io.*;
import java.util.*;

// Main class
class GFG {

  // Main driver method
  public static void main(String[] args) {

    // Try block to check for exceptions
    try {

      // Creating an object of Arraylist class
      ArrayList<String> list = new ArrayList<>();


      // Adding elements to the List
      // using add() method

      // Custom input elements
      list.add("A");
      list.add("B");å
      list.add("C");
      list.add("D");

      // Print all the elements added in the above object
      System.out.println(list);

      
      // Setting the element at the 6 th index which
      // does not exist in our input list object 
      list.set(6);
  
      // Printing the newly updated List
      System.out.println(list);
    }

    // Catch block to handle the exceptions
    catch (Exception e) {

      // Display the exception on the console
      System.out.println(e);
    }
  }
}

Output: