Selection Sort in Java

Last Updated: 06 October, 2024 🕓 5 Mins

Sorting is the process of arranging a list of unsorted data in a particular order, either ascending or descending. Sort algorithms play a very crucial role for organizing unsorted data and facilitating efficient searching, retrieval, and analysis.

Every sorting algorithm has a unique approach for sorting the data; these sorting algorithms are used according to the specific requirements of the problem, including data size, structure, and distribution, as well as time and space constraints.

In this tutorial, we are going to learn all about Selection Sort in Java.

What is a Selection Sort Algorithm?

Selection Sort is a simple and efficient sorting algorithm used to sort a list of unsorted elements in a particular order, either ascending or descending.

In selection sort, the first element in the list is selected, and it is compared repeatedly with all the remaining elements one by one in the list. If any element is smaller than the selected element (for ascending order), then both are swapped so that the first position is filled with the smallest element in the sorted order. Next, we select the element at a second position in the list, and it is compared with all the remaining elements in the list. If any element is smaller than the selected element, then both are swapped. This procedure is repeated until the entire list is sorted.

How does Selection Sort Algorithm work?

Java program for implementation of Selection Sort

  public class SelectionSortExample {
    // Function for sorting an array
    void sort(int array[]) {
      // Storing array length
      int length = array.length;
  
      // One by one move boundary of unsorted sub array
      for (int i = 0; i < length - 1; i++) {
        // Find the minimum element in unsorted array
        int min_idx = i;
        for (int j = i + 1; j < length; j++)
          if (array[j] < array[min_idx])
            min_idx = j;
  
        // Swap the found minimum element with the first element
        int temp = array[min_idx];
        array[min_idx] = array[i];
        array[i] = temp;
      }
    }
  
    // Function to prints the array
    void printArray(int array[]) {
      for (int i = 0; i < array.length; ++i)
        System.out.print(array[i] + " ");
      System.out.println();
    }
  
    public static void main(String args[]) {
      SelectionSortExample ssObject = new SelectionSortExample();
      
      // Create an unsorted array
      int array[] = { 40, 70, 90, 20, 80, 100, 60, 10, 30, 50 };
      System.out.println("BEFORE calling sort method, Array elements: ");
      ssObject.printArray(array);
      
      // Calling a method to sort the array
      ssObject.sort(array);
      System.out.println("\nAFTER calling sort method, Array elements: ");
      
      // Calling a method to print the array
      ssObject.printArray(array);
    }
  }

BEFORE calling sort method, Array elements:
40 70 90 20 80 100 60 10 30 50

AFTER calling sort method, Array elements:
10 20 30 40 50 60 70 80 90 100

Difference between Selection Sort and Bubble Sort:

Selection Sort and Bubble Sort are sorting algorithms used to sort an unsorted list of elements; both follow different approaches to sort a list and have many key differences.

When is it best choice to use Selection Sort?

Selection sort is the best and most suitable for small datasets, memory-constrained environments (memory usage needs to be minimal), and educational purposes.

Feature	Selection Sort	Bubble Sort
Approach	Finds the minimum/maximum and swaps	Compares and swaps adjacent elements
Swaps	Fewer swaps	More frequent swaps
Efficiency	In terms of swap, more efficient	Less efficient
Time Complexity	O(n^2) in average and worst cases	O(n^2) in average and worst cases