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.

Table of Contents

## 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.

```
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:

```
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.