Below is a Java program that finds the second-largest and second-smallest elements in an ArrayList of integers:


import java.util.ArrayList; 
import java.util.Collections; 
import java.util.List; 
public class SecondLargestSmallest {
public static void main(String[] args) { 
 List<Integer> numbers = new ArrayList<>();
 numbers.add(10);
 numbers.add(5);
 numbers.add(20);
 numbers.add(15);
 numbers.add(25); 
int secondLargest = findSecondLargest(numbers);
int secondSmallest = findSecondSmallest(numbers);
 System.out.println("List: " + numbers);
 System.out.println("Second Largest: " + secondLargest);
 System.out.println("Second Smallest: " + secondSmallest);
 } 
public static int findSecondLargest(List<Integer> numbers) {
 Collections.sort(numbers); 
return numbers.get(numbers.size() - 2); 
 } 
public static int findSecondSmallest(List<Integer> numbers) {
 Collections.sort(numbers);
return numbers.get(1); 
 } 
}

Explanation:

  1. We define a class called SecondLargestSmallest.
  2. In the main method, we create an ArrayList called numbers containing some integers. You can modify this list with your desired input elements.
  3. We call two methods, findSecondLargest and findSecondSmallest, to get the second-largest and second-smallest elements from the numbers list.
  4. Both methods use Collections.sort() to sort the list in ascending order. After sorting, the second-largest element will be at the index (numbers.size() - 2), and the second-smallest element will be at index 1.
  5. The findSecondLargest method returns the second-largest element, and the findSecondSmallest method returns the second-smallest element.
  6. Finally, the main method prints the original list and the second-largest and second-smallest elements.

Output will be:

List: [10, 5, 20, 15, 25]

Second Largest: 20

Second Smallest: 10

Please note that if the list contains duplicate elements, the program considers the second-largest and second-smallest elements without eliminating duplicates. For instance, in the above example, there are two occurrences of 20 (the largest element), but we still consider 20 as the second-largest element. Similarly, there are two occurrences of 10 (the smallest element), but we still consider 10 as the second-smallest element.