Collections swap() method in Java with Examples

Last Updated : 23 Jan, 2026

The swap() method of java.util.Collections is used to exchange elements at two specified positions in a list. It works with any class that implements the List interface.

  • If both positions are the same, the list remains unchanged
  • Works with ArrayList, LinkedList, Vector, etc.
  • Operates directly on the original list (in-place)
Java 
import java.util.*;

public class Demo {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3);
        Collections.swap(list, 0, 2);
        System.out.println(list);
    }
}

Output
[3, 2, 1]

Explanation: The swap() method exchanges the elements at index 0 and index 2. All other elements in the list remain unchanged.

Syntax 

public static void swap(List<?> list, int i, int j)

Parameters

  • list -The list in which the elements are to be swapped.
  • i - The index of the first element.
  • j - The index of the second element.

Below are the examples to illustrate the swap() method

Example 1: Swapping Elements in a List

Java 
import java.util.*;
public class GFG1 {
    public static void main(String[] args) {

        try {
            List<String> list = new ArrayList<>();
            list.add("A");
            list.add("B");
            list.add("C");
            list.add("D");
            list.add("E");

            System.out.println("Before swap: " + list);
            Collections.swap(list, 0, 4);
            System.out.println("After swap: " + list);
        }
        catch (IndexOutOfBoundsException e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

Output
Before swap: [A, B, C, D, E]
After swap: [E, B, C, D, A]

Explanation: The swap() method exchanges the elements located at index 0 and index 4 in the list.All remaining elements retain their original positions.

Example 2: IndexOutOfBoundsException

Java 
import java.util.*;
public class GFG2 {
    public static void main(String[] args) {

        try {
            List<String> list = new ArrayList<>();

            list.add("A");
            list.add("B");
            list.add("C");
            list.add("D");
            list.add("E");
            System.out.println("Before swap: " + list);
            Collections.swap(list, 0, 5);
        }
        catch (IndexOutOfBoundsException e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

Output
Before swap: [A, B, C, D, E]
Exception thrown: java.lang.IndexOutOfBoundsException: Index 5 out of bounds for length 5

Explanation: The method attempts to swap elements using an index that exceeds the list size. As a result, an IndexOutOfBoundsException is thrown at runtime.

Note:

  • swap() operates in constant time for most List implementations.
  • The list must be modifiable.
  • No changes occur if both indices are the same.
  • Useful for sorting algorithms, shuffling, and DSA problems.
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