Collections swap() method in Java with Examples

The swap() method of java.util.Collections class is used to swap the elements at the specified positions in the specified list. If the specified positions are equal, invoking this method leaves the list unchanged.

Syntax:

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

Parameters: This method takes the following argument as a Parameter  

• list – The list in which to swap elements.
• i – the index of one element to be swapped.
• j – the index of the other element to be swapped.

Exception This method throws IndexOutOfBoundsException, if either i or j is out of range (i = list.size() || j = list.size()).

Below are the examples to illustrate the swap() method

Example 1:

Java

// Java program to demonstrate
// swap() method for String value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // creating object of List<String>
            List<String> vector = new ArrayList<String>();

            // populate the vector
            vector.add("A");
            vector.add("B");
            vector.add("C");
            vector.add("D");
            vector.add("E");

            // printing the vector before swap
            System.out.println("Before swap: " + vector);

            // swap the elements
            System.out.println("\nSwapping 0th and 4th element.");
            Collections.swap(vector, 0, 4);

            // printing the vector after swap
            System.out.println("\nAfter swap: " + vector);
        }

        catch (IndexOutOfBoundsException e) {
            System.out.println("\nException thrown : " + e);
        }
    }
}

Output:

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

Swapping 0th and 4th element.

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

Example 2: For IndexOutOfBoundsException

Java

// Java program to demonstrate
// swap() method for IndexOutOfBoundsException

import java.util.*;

public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
        try {

            // creating object of List<String>
            List<String> vector = new ArrayList<String>();

            // populate the vector
            vector.add("A");
            vector.add("B");
            vector.add("C");
            vector.add("D");
            vector.add("E");

            // printing the vector before swap
            System.out.println("Before swap: " + vector);

            // swap the elements
            System.out.println("\nTrying to swap elements"
                               + " more than upper bound index ");
            Collections.swap(vector, 0, 5);

            // printing the vector after swap
            System.out.println("After swap: " + vector);
        }

        catch (IndexOutOfBoundsException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

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

Trying to swap elements more than upper bound index 
Exception thrown : java.lang.IndexOutOfBoundsException: Index: 5, Size: 5