Selection Sort in Java: Step‑by‑Step Example & Full Code

What Is Selection Sort?

Selection Sort is a straightforward comparison‑based algorithm that repeatedly selects the smallest remaining element and swaps it into place. While not the fastest for large data sets, its simplicity makes it ideal for educational purposes and small arrays.

How the Algorithm Works

• Start at the beginning of the array.
• Find the smallest element in the unsorted portion.
• Swap it with the element at the current position.
• Move the boundary between sorted and unsorted sections one step to the right.
• Repeat until the entire array is sorted.

Java Implementation

Below is a concise Java program that demonstrates the selection sort algorithm on an integer array. The code prints the array before and after sorting, as well as the intermediate steps to illustrate each pass.

package com.guru99;

public class SelectionSortAlgo {

    public static void main(String[] args) {
        int[] myArray = {860, 8, 200, 9};

        System.out.println("------Before Selection Sort-----");
        printArray(myArray);

        selection(myArray); // Sort the array

        System.out.println("-----After Selection Sort-----");
        printArray(myArray);
    }

    public static void selection(int[] array) {
        for (int i = 0; i < array.length - 1; i++) {
            System.out.println("Sort Pass Number " + (i + 1));
            int index = i;

            for (int j = i + 1; j < array.length; j++) {
                System.out.println("Comparing " + array[index] + " and " + array[j]);
                if (array[j] < array[index]) {
                    System.out.println(array[index] + " is greater than " + array[j]);
                    index = j;
                }
            }

            int smallerNumber = array[index];
            array[index] = array[i];
            array[i] = smallerNumber;

            System.out.println("Swapping Elements: New Array After Swap");
            printArray(array);
        }
    }

    private static void printArray(int[] array) {
        for (int i = 0; i < array.length; i++) {
            System.out.print(array[i] + " ");
        }
        System.out.println();
    }
}

Sample Output

------Before Selection Sort-----
860 8 200 9 
Sort Pass Number 1
Comparing 860 and 8
860 is greater than 8
Comparing 8 and 200
Comparing 8 and 9
Swapping Elements: New Array After Swap
8 860 200 9 
Sort Pass Number 2
Comparing 860 and 200
860 is greater than 200
Comparing 200 and 9
200 is greater than 9
Swapping Elements: New Array After Swap
8 9 200 860 
Sort Pass Number 3
Comparing 200 and 860
Swapping Elements: New Array After Swap
8 9 200 860 
-----After Selection Sort-----
8 9 200 860 

Performance Notes

Selection Sort performs O(n²) comparisons regardless of input and uses at most O(1) additional memory. Its deterministic behavior makes it suitable for environments where memory is constrained.