Below is a Java program to reverse the elements in an ArrayList of integers:


import java.util.ArrayList;
import java.util.Collections; 
import java.util.Scanner; 
public class ReverseArrayList { 
public static void main(String[] args) {
// Create an ArrayList of integers 
 ArrayList<Integer> numbersList = new ArrayList<>();
numbersList.add(5);
numbersList.add(50);
numbersList.add(15);
numbersList.add(25);
 numbersList.add(5);
 // Reverse the elements in the ArrayList

        Collections.reverse(numbersList); 
// Print the ArrayList after reversing 
 System.out.println("ArrayList after reversing: " + numbersList);
    }
 }

 

Example usage:

ArrayList after reversing: [5,25,15,50,5]

Explanation:

  1. We start by creating an ArrayList of integers called numbersList.
  2. The user is prompted to input integers to add to the list, and the input loop continues until the user enters -1.
  3. After adding elements to the ArrayList, we use the Collections.reverse() method to reverse the elements in the list.
  4. The reverse() method modifies the original ArrayList in place and reverses the order of elements.
  5. Finally, we print the ArrayList after reversing the elements.

The Collections.reverse() method provides a convenient way to reverse the elements in an ArrayList without requiring a custom implementation using loops. It efficiently reverses the elements in linear time.