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 which 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 which 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);


      // Settijg 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: