Java BMI Calculator: Calculate Your Body Mass Index (BMI)

BMI Calculator - Simple BMI Calculator:

BMI Calculator :

Calculate Body Mass Index based on user input for weight and height.

The Body Mass Index (BMI) calculator takes user input for weight and height and calculates the BMI using a formula. Based on the result, it classifies the user as underweight, normal weight, overweight, or obese.

Input: Weight (kg) and height (m).
Output: BMI value and corresponding category (e.g., underweight, normal, overweight).

Example:

• Input: Weight = 70 kg, Height = 1.75 m
• Output: BMI = 22.86 (Normal weight)

Solution 1: BMI Calculator using Basic Java

Code:

import java.util.Scanner;

public class BMICalculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in); // Initialize scanner to take user input

        // Take user input for weight in kilograms
        System.out.println("Enter your weight in kilograms (kg): ");
        double weight = scanner.nextDouble(); 

        // Take user input for height in meters
        System.out.println("Enter your height in meters (m): ");
        double height = scanner.nextDouble(); 

        // Calculate BMI using the formula: BMI = weight / (height * height)
        double bmi = weight / (height * height);

        // Display the calculated BMI
        System.out.printf("Your BMI is: %.2f\n", bmi);

        // Determine the BMI category based on the value
        if (bmi < 18.5) {
            System.out.println("You are underweight.");
        } else if (bmi >= 18.5 && bmi < 24.9) {
            System.out.println("You have a normal weight.");
        } else if (bmi >= 25 && bmi < 29.9) {
            System.out.println("You are overweight.");
        } else {
            System.out.println("You are obese.");
        }

        scanner.close(); // Close the scanner
    }
} 

Output:

Enter your weight in kilograms (kg): 
 76
Enter your height in meters (m): 
 2.2
Your BMI is: 15.70
You are underweight.

Explanation :

• Input Handling: Takes weight and height from the user using the Scanner class.
• BMI Calculation: Computes BMI using the formula BMI = weight / (height * height).
• Result Formatting: Displays BMI to two decimal places using printf.
• Categorization: Uses conditional statements to determine and display the BMI category.
• Output: Prints the BMI value along with the corresponding weight category (underweight, normal, overweight, or obese).

Solution 2: BMI Calculator with Error Handling and Improved Input Validation

Code:

import java.util.Scanner;

public class BMICalculatorWithValidation {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in); // Initialize scanner for user input
        double weight = 0, height = 0;

        // Input weight with validation
        while (true) {
            System.out.println("Enter your weight in kilograms (kg): ");
            if (scanner.hasNextDouble()) {
                weight = scanner.nextDouble();
                if (weight > 0) {
                    break; // Valid weight entered
                } else {
                    System.out.println("Weight must be greater than zero.");
                }
            } else {
                System.out.println("Please enter a valid number for weight.");
                scanner.next(); // Clear the invalid input
            }
        }

        // Input height with validation
        while (true) {
            System.out.println("Enter your height in meters (m): ");
            if (scanner.hasNextDouble()) {
                height = scanner.nextDouble();
                if (height > 0) {
                    break; // Valid height entered
                } else {
                    System.out.println("Height must be greater than zero.");
                }
            } else {
                System.out.println("Please enter a valid number for height.");
                scanner.next(); // Clear the invalid input
            }
        }

        // Calculate BMI using the formula
        double bmi = weight / (height * height);

        // Display the BMI value
        System.out.printf("Your BMI is: %.2f\n", bmi);

        // Display BMI category based on the BMI value
        if (bmi < 18.5) {
            System.out.println("You are underweight.");
        } else if (bmi >= 18.5 && bmi < 24.9) {
            System.out.println("You have a normal weight.");
        } else if (bmi >= 25 && bmi < 29.9) {
            System.out.println("You are overweight.");
        } else {
            System.out.println("You are obese.");
        }

        scanner.close(); // Close the scanner
    }
}  

Output:

Enter your weight in kilograms (kg): 
 76
Enter your height in meters (m): 
 1.9
Your BMI is: 21.05
You have a normal weight.

Explanation:

• Input Validation: Ensures valid numeric input for weight and height, prompting the user to re-enter values if invalid.
• Error Handling: Verifies that both weight and height are positive values before proceeding with BMI calculation.
• BMI Calculation: Uses the same formula as the first solution to compute BMI.
• Result Output: Displays BMI to two decimal places and the corresponding weight category.
• User-Friendly: Provides clear error messages and handles invalid input gracefully, improving user experience.

Java Code Editor: