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Operators & Expressions

Java Program: BMI Category Classification Using Chained Ternary

BMI Formula

BMI Categories

import java.util.Scanner;
 
public class BMICalculator {
    public static void main(String[] args) {
 
        Scanner sc = new Scanner(System.in);
 
        System.out.print("Enter weight in kg: ");
        double weight = sc.nextDouble();
 
        System.out.print("Enter height in meters: ");
        double height = sc.nextDouble();
 
        double bmi = weight / (height * height);
 
        // Chained ternary operator for BMI classification
        String category = (bmi < 18.5) ? "Underweight" :
                          (bmi < 25)   ? "Normal" :
                          (bmi < 30)   ? "Overweight" :
                                         "Obese";
 
        System.out.println("\n------ BMI Result ------");
        System.out.printf("BMI Value : %.2f%n", bmi);
        System.out.println("Category  : " + category);
 
        sc.close();
    }
}

 
OUTPUT 1:

INPUT : 
Enter weight in kg: 60
Enter height in meters: 1.70

OUTPUT : 
------ BMI Result ------
BMI Value : 20.76
Category  : Normal


OUTPUT 2:

INPUT : 
Enter weight in kg: 85
Enter height in meters: 1.65

OUTPUT : 
------ BMI Result ------
BMI Value : 31.22
Category  : Obese

Explanation

1. BMI Calculation

double bmi = weight / (height * height);

• Uses the standard BMI formula.
• double ensures decimal precision.

2. Chained Ternary Operator

String category = (bmi < 18.5) ? "Underweight" :

                  (bmi < 25)   ? "Normal" :

                  (bmi < 30)   ? "Overweight" :

                                 "Obese";

Equivalent if–else logic:

if (bmi < 18.5)

    category = "Underweight";

else if (bmi < 25)

    category = "Normal";

else if (bmi < 30)

    category = "Overweight";

else

    category = "Obese";

✔ Demonstrates compact decision-making
✔ Uses multiple conditions in a single expression

3. Output Formatting

System.out.printf("BMI Value : %.2f%n", bmi);

• Displays BMI up to 2 decimal places.

✅ Key Concepts Used

✔ Arithmetic expressions
✔ Chained ternary operator (?:)
✔ Conditional logic without if–else
✔ User input using Scanner
✔ Formatted output

📌 Short Exam Answer

This program calculates BMI using height and weight, then classifies it into categories using a chained ternary operator, demonstrating concise conditional evaluation.