Selection Sort in Java

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?

The following steps are used to carry out the selection sort algorithm:

• Step 1: Select the first element of the list.

• Step 2: Compare the selected element with all the other elements one by one in the list.

• Step 3: In each comparision of elements, if any element is found smaller than the selected element (for Ascending order), then both are swapped.

• Step 4: Repeat the same procedure with element in the next position in the list till the entire list is sorted.

A simple Java program of Selection sort is given below for understanding.

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.

In the given table below, summarizing the key differences between both:

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.