Java Data Structures - Bubble Sort

Sorting refers to arranging data in a particular format. Sorting algorithm specifies the way to arrange data in a particular order. Most common orders are in numerical or lexicographical order.

The importance of sorting lies in the fact that data searching can be optimized to a very high level, if data is stored in a sorted manner. Sorting is also used to represent data in more readable formats. Following are some of the examples of sorting in real-life scenarios.

• Telephone Directory − The telephone directory stores the telephone numbers of people sorted by their names, so that the names can be searched easily.

• Dictionary − The dictionary stores words in an alphabetical order so that searching of any word becomes easy.

In-place Sorting and Not-in-place Sorting

Sorting algorithms may require some extra space for comparison and temporary storage of few data elements. These algorithms do not require any extra space and sorting is said to happen in-place, or for example, within the array itself. This is called in-place sorting. Bubble sort is an example of in-place sorting.

However, in some sorting algorithms, the program requires space which is more than or equal to the elements being sorted. Sorting which uses equal or more space is called not-in-place sorting. Merge-sort is an example of not-in-place sorting.

The Bubble Sort in Java

Bubble sort is a simple sorting algorithm. This sorting algorithm is comparison-based algorithm in which each pair of adjacent elements is compared and the elements are swapped if they are not in order. This algorithm is not suitable for large data sets as its average and worst case complexity are of Ο(n2) where n is the number of items.

Algorithm

We assume list is an array of n elements. We further assume that swap() function swaps the values of the given array elements.

Step 1: Assume i is the first element of the list then, compare the elements i and i+1. (first two elements of the array)
Step 2: If the i (first element) is greater than the second (i+1) swap them.
Step 3: Now, increment the i value and repeat the same.(for 2nd and 3rd elements) 
Step 4: Repeat this till the end of the array.

Example

import java.util.Arrays;
public class BubbleSort {
   public static void main(String args[]) {
      int[] myArray = {10, 20, 65, 96, 56};      
      System.out.println("Contents of the array before sorting : ");
      System.out.println(Arrays.toString(myArray));
      
      int n = myArray.length;
      int temp = 0;
      
      for(int i = 0; i<n-1; i++) {
         for(int j = 0; j<n-1; j++) {
            if (myArray[j] > myArray[j+1]) {
               temp = myArray[i];
               myArray[j] = myArray[j+1];
               myArray[j+1] = temp;
            }
         }         
      }           
      System.out.println("Contents of the array after sorting : ");
      System.out.println(Arrays.toString(myArray));       
   }
}

Output

Contents of the array before sorting : 
[10, 20, 65, 96, 56]
Contents of the array after sorting : 
[10, 10, 20, 10, 20]