” The algorithm finds the minimum value, swaps it with the value in the first position, and repeats these steps for the remainder of the list. It does no more than n swaps, and thus is useful where swapping is very expensive. “

Selection Sort, Wikipedia

When you are learning Java you are very likely going to be asked to write a program to sort values. We will start with one of the simpler sort algorithms, the Selection Sort (also known as an Exchange Sort). It’s not a particularly efficient algorithm and really only suitable for small lists.

package com.learnjava.math.sort;

import java.util.Random;

/**
 * Write a program to sort an array of numbers using a Selection Sort
 * Also known as an Exchange Sort
 *
 * @author https://learn-java-by-example.com
 *
 */
public class SelectionSort {

	public static void main(String[] args) {

		// Create an array of random numbers to sort

		int[] data = generateData();

		// Display the unsorted data

		System.out.println("Unsorted data:");
		printArray(data);

		// Sort the array

		sortArray(data);

		// Display the sorted data

		System.out.println("Sorted data:");
		printArray(data);
	}

	private static void sortArray(int[] data) {

		// Loop through the array,
		// comparing each value with each of the following values

		for (int i=0; i<data.length-1; i++) {
			for (int j=i+1; j<data.length; j++) {

				// Check if the value needs to be swapped or not

				if (data[i] < data[j]) {

					// Swap values

					int temp = data[i];
					data[i] = data[j];
					data[j] = temp;
				}
			}

			// Print out the array after we have
			// finished each element to see the progress

			System.out.println("Loop " + i);
			printArray(data);
		}
	}

	private static int[] generateData() {
		Random random = new Random();

		int[] data = new int[10];
		for (int i=0; i<data.length; i++) {
			data[i] = random.nextInt(100);
		}
		return data;
	}

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