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How to Replace a Element in Java ArrayList?

  • Last Updated : 27 Jul, 2021

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:

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