Java Program to Find the Second Largest Number in an Array

Introduction

Finding the second largest number in an array is a common task in programming, particularly in data analysis and algorithm development. This guide will show you how to create a Java program that finds the second-largest number in a given array of integers.

Problem Statement

Create a Java program that:

• Takes an array of integers as input.
• Finds and returns the second largest number in the array.
• Handles arrays with duplicate values appropriately.

Example 1:

• Input: [3, 5, 7, 1, 4]
• Output: The second largest number is 5

Example 2:

• Input: [10, 20, 20, 5, 8]
• Output: The second largest number is 10

Solution Steps

1. Initialize Two Variables: Use two variables to keep track of the largest and second largest numbers.
2. Iterate Through the Array: Loop through the array to update the largest and second-largest values.
3. Handle Edge Cases: Ensure that the program correctly handles arrays with less than two elements.
4. Display the Result: Print the second largest number.

Java Program

Java Program to Find the Second Largest Number in an Array

import java.util.Scanner;

/**
 * Java Program to Find the Second Largest Number in an Array
 * Author: https://www.javaguides.net/
 */
public class SecondLargestNumber {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Step 1: Prompt the user for input
        System.out.print("Enter the number of elements in the array: ");
        int n = scanner.nextInt();

        if (n < 2) {
            System.out.println("Array must contain at least two elements.");
            return;
        }

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

        // Step 2: Find the second largest number
        int largest = Integer.MIN_VALUE;
        int secondLargest = Integer.MIN_VALUE;

        for (int i = 0; i < n; i++) {
            if (array[i] > largest) {
                secondLargest = largest;
                largest = array[i];
            } else if (array[i] > secondLargest && array[i] != largest) {
                secondLargest = array[i];
            }
        }

        // Step 3: Display the result
        if (secondLargest == Integer.MIN_VALUE) {
            System.out.println("No second largest element found.");
        } else {
            System.out.println("The second largest number is " + secondLargest);
        }
    }
}

Explanation

• Input: The program prompts the user to enter the number of elements in the array and the elements themselves.

• Finding the Second Largest:

  • Two variables, largest and secondLargest, are initialized to the smallest possible integer value (Integer.MIN_VALUE).
  • As the program iterates through the array:
    • If the current element is greater than largest, secondLargest is updated to largest, and largest is updated to the current element.
    • If the current element is greater than secondLargest but not equal to largest, secondLargest is updated to the current element.

• Edge Case Handling: If the array has fewer than two elements, the program immediately informs the user and terminates. If there is no second-largest number (e.g., all elements are the same), the program outputs an appropriate message.

• Output: The program prints the second-largest number found in the array.

Output Example

Example 1:

Enter the number of elements in the array: 5
Enter the elements of the array:
3
5
7
1
4
The second largest number is 5

Example 2:

Enter the number of elements in the array: 5
Enter the elements of the array:
10
20
20
5
8
The second largest number is 10

Example 3:

Enter the number of elements in the array: 2
Enter the elements of the array:
5
5
No second largest element found.

Explanation of Edge Cases:

• Example 1: The array has distinct elements, and the second largest is correctly identified as 5.
• Example 2: The array has duplicate elements, but the program correctly identifies the second largest as 10.
• Example 3: The array has duplicate elements only, so no second largest is found.

Conclusion

This Java program efficiently finds the second-largest number in an array by maintaining two variables for the largest and second-largest values. The program handles arrays with duplicate elements and correctly outputs the second-largest number or an appropriate message if no such number exists. This approach is robust and can be applied to various scenarios where identifying the second-largest element is required.