Bubble Sort Program in Java (With Explanation & Dry Run)

Introduction

Bubble Sort is one of the simplest sorting techniques in Java. It is commonly asked in BCA exams, practicals, and viva to test understanding of loops and arrays.

In this article, you will learn:

• What is Bubble Sort

• How Bubble Sort works

• Bubble Sort program in Java

• Step-by-step dry run

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❓ What Is Bubble Sort?

Bubble Sort is a sorting algorithm that repeatedly compares adjacent elements and swaps them if they are in the wrong order.

👉 Larger elements “bubble up” to the end of the array, just like air bubbles rise in water.

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🧠 How Bubble Sort Works

1. Compare first and second element

2. Swap if first > second

3. Move to next pair

4. Repeat passes until array is sorted

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🧩 Algorithm for Bubble Sort

1. Start

2. Read array elements

3. Repeat for passes from 0 to n-1

4. Compare adjacent elements

5. Swap if they are in wrong order

6. Print sorted array

7. End

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💻 Bubble Sort Program in Java

import java.util.Scanner;

public class BubbleSort {
    public static void main(String[] args) {
        int n, temp;

        Scanner sc = new Scanner(System.in);
        System.out.print("Enter number of elements: ");
        n = sc.nextInt();

        int[] arr = new int[n];

        System.out.println("Enter array elements:");
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
        }

        // Bubble Sort Logic
        for (int i = 0; i < n - 1; i++) {
            for (int j = 0; j < n - 1 - i; j++) {
                if (arr[j] > arr[j + 1]) {
                    temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                }
            }
        }

        System.out.println("Sorted Array:");
        for (int i = 0; i < n; i++) {
            System.out.print(arr[i] + " ");
        }
    }
}

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🧪 Dry Run

Input

Array = {5, 3, 1}

Pass 1

• Compare 5 & 3 → swap → {3, 5, 1}

• Compare 5 & 1 → swap → {3, 1, 5}

Pass 2

• Compare 3 & 1 → swap → {1, 3, 5}

Final Sorted Array

1 3 5

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🖥️ Output

Enter number of elements: 3
Enter array elements:
5 3 1
Sorted Array:
1 3 5

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📌 Important Points for Exams

• Bubble Sort uses nested loops

• Time Complexity:

  • Worst case: O(n²)

  • Best case: O(n) (optimized version)

• Space Complexity: O(1)

• Easy but not efficient for large data

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📊 Advantages & Disadvantages

✅ Advantages

• Easy to understand

• Simple implementation

• Good for small data

❌ Disadvantages

• Very slow for large arrays

• Not used in real-world applications