Bubble Sort in Java

Java Sorting is one of the many aspects of java interview questions. In this post, we will see java bubble sort example and write a program for bubble sort.

Bubble sort is also known as the exchange sort. It is the simplest algorithm for sorting numbers.

Bubble Sort Algorithm

• In bubble sort, the array of integers is traversed from index 0 to length-1.
• The value at 0th position is compared with the value at 1st position and if the later is small, it’s swapped.
• The comparison is moved from the 0th index to length-1 index so that after the first iteration, the last index has the biggest value.
• The same process is repeated again from 0th to length-1 index. After (length-1) iteration, the array is sorted.
• In worst-case, the complexity of bubble sort is O(n2) and in best-case, the complexity of bubble sort is Ω(n).

Bubble Sort in Java

Here is the implementation of Bubble Sort in Java program.

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import java.util.Arrays;

public class BubbleSort {

	public static void main(String args[]) {
		int arr[] = { 5,4,3,2,1 };
		int arr1[] = { 1,2,3,4,5 };
		System.out.println("Array after sorting in ascending order:"+Arrays.toString(bubbleSortAscending(arr)));
		System.out.println("Array after sorting in descending order:"+Arrays.toString(bubbleSortDescending(arr1)));
	}
	
	public static int[] bubbleSortAscending(int[] arr){
		int temp;
		for(int i=0; i < arr.length-1; i++){
			
			for(int j=1; j < arr.length-i; j++){
				if(arr[j-1] > arr[j]){
					temp=arr[j-1];
					arr[j-1] = arr[j];
					arr[j] = temp;
				}
			}
			//check that last index has highest value in first loop,
			// second last index has second last highest value and so on
			System.out.println("Array after "+(i+1)+"th iteration:"+Arrays.toString(arr));
		}
		return arr;
	}
	
	public static int[] bubbleSortDescending(int[] arr){
		int temp;
		for(int i=0; i < arr.length-1; i++){
			
			for(int j=1; j < arr.length-i; j++){
				if(arr[j-1] < arr[j]){
					temp=arr[j-1];
					arr[j-1] = arr[j];
					arr[j] = temp;
				}
			}
			//check that last index has highest value in first loop,
			// second last index has second last highest value and so on
			System.out.println("Array after "+(i+1)+"th iteration:"+Arrays.toString(arr));
		}
		return arr;
	}

}

The above program is for sorting in ascending as well as descending order using bubble sort algorithm.

Output of the above program is:

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Array after 1th iteration:[4, 3, 2, 1, 5]
Array after 2th iteration:[3, 2, 1, 4, 5]
Array after 3th iteration:[2, 1, 3, 4, 5]
Array after 4th iteration:[1, 2, 3, 4, 5]
Array after sorting in ascending order:[1, 2, 3, 4, 5]
Array after 1th iteration:[2, 3, 4, 5, 1]
Array after 2th iteration:[3, 4, 5, 2, 1]
Array after 3th iteration:[4, 5, 3, 2, 1]
Array after 4th iteration:[5, 4, 3, 2, 1]
Array after sorting in descending order:[5, 4, 3, 2, 1]

As we can see that in every iteration, the last index is getting sorted and it takes (array length – 1) iterations for sorting.

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