Bubble Sort in Java
Bubble sort in Java is the simplest, comparisonbased sorting algorithm which helps us sort an array by traversing it repeatedly, comparing adjacent elements, and swapping them based upon desired sorting criteria. Bubble sort is an inplace algorithm, meaning it does not require extra space; it changes the original array instead.
For more understanding, you may read more about Bubble Sort Algorithm.
Algorithm for Bubble Sort in Java
Using the bubble sort algorithm, we can sort an unsorted array A of size N in increasing order in three simple steps. Traverse the array N1 times and follow the steps.
 Starting with the very first element of the array, compare the current element with the next consecutive element.
 If the current element A[i] is greater than the next element A[i+1], swap them, move to the next element, and repeat step 2.
 Otherwise, move to the next element and repeat step 2.
Bubble Sort Example
Let's take an unsorted array A = [7,11,9,2,4] containing five elements. We will sort it in increasing order using the Bubble sort in Java. Our desired output is [2,4,7,9,11].
To sort the array, we need a total of 4 (N1) passes indexed from 0 to 3.
Let's walk through the algorithm step by step.
First pass (PassNum = 0)

index = 0, we compare A[0] and A[1] since 7 < 11, so there is no change in the array, and we move to the next element.

index = 1, A[1] which is 11 is greater than A[2] which is 9 so we swap A[1] and A[2], the array becomes [7,9,11,2,4] and we move to the next element.

index = 2, compare A[2] with A[3], 11 > 2 so A[2] and A[3] are swapped and the array becomes [7,9,2,11,4] and we move to next element.

index = 3, compare A[3] with A[4], 11 > 4 so A[3] and A[4] switch their places resulting the array as [7,9,2,4,11].
End of the first pass, we compared all five elements in pairs by iterating till the second last element, and as a result, 11 is pushed to its desired position, and the array is [7,9,2,4,11] now.
Second pass (PassNum = 1)

index = 0, we compare A[0] and A[1], since 7 < 9, so there is no change in the array, we move to the next element.

index = 1, A[1] is 9 is greater than A[2] is 2 so we swap A[1] and A[2], the array becomes [7,2,9,4,11] and we move to the next element.

index = 2, compare A[2] with A[3], 9 > 4 so A[2] and A[3] are swapped and the array becomes [7,2,4,9,11].
At the end of the second pass, we compared all four remaining unsorted elements (11 were sorted in the first pass) in pairs by iterating until the second last element. As a result, 9 (the largest of the remaining 4 elements) is pushed to its desired position, and the array is [7,2,4,9,11] now.
Third pass (PassNum = 2)

index = 0, A[0] which is 7 is greater than A[1] that is 2 so we swap A[0] and A[1], the array becomes [2,7,4,9,11] and we move to the next element.

index = 1, compare A[1] with A[2], 7 > 4 so A[2] and A[3] are swapped and the array becomes [2,4,7,9,11].
At the end of the third pass, we have compared all three remaining unsorted elements (9 and 11 were sorted earlier) in pairs by iterating until the second last element. As a result, 7 (the largest of the remaining three elements) is pushed to its desired position, and the array is [2,4,7,9,11] now.
Fourth pass (PassNum = 3)

index = 0, we compare A[0] and A[1], since 2 < 4, so no change in the array.
At the end of the fourth pass, even though the array was sorted in the third pass, we don't have a way to check if it's sorted and end the loop. As a result, we had to complete the maximum number of N1 passes possible.
Implementation of Bubble Sort in Java
The below Java program is the implementation of a bubble given unsorted array A of length N.
Complexity Analysis
Time complexity:
 Worst Case: O($N^2$)
 Best Case: O(N)
Space Complexity:
 O(1)
Advantage of Bubble Sort in Java
 The bubble sort's main advantage is that it is widely used and simple to implement.
 In its bestcase scenario, which checks whether the array is already sorted, the optimized algorithm is highly efficient.
 Bubble sort is an inplace sorting technique, which means it does not require additional space to sort the array; it can modify the original array.
Conclusion
 Bubble sort is a sorting algorithm used to sort an array.
 Its time complexity is O(N2).
 Bubble sort is an inplace sorting algorithm.