How to swap two items in ArrayList in Java

The following code swaps; two elements in an ArrayList. You can swap two items by calling the Collections.swap(int i1, int i2) . You must pass as arguments the indices of the two objects to be swapped.

import java.util.ArrayList; 
import java.util.Collections; 
 
public class swap {
 
 public static void main(String a[]){
 ArrayList arlist = new ArrayList(); 

 arlist.add("o1"); 
 arlist.add("o2"); 
 arlist.add("o3"); 
 arlist.add("o4"); 
 
 System.out.println("Before: "+arlist); 

 //swap the two objects at index 1 and 3
 //o2 and o4
 Collections.swap(arlist, 1, 3); 
 
 System.out.println("After: "+arlist); 
 
 }
}

Result:

Before: [o1, o2, o3, o4]
After: [o1, o4, o3, o2]

Reference:
javadoc: Collections.swap()