Here's a detailed explanation and corrected answer you can post on StackOverflow:
You're experiencing the issue because of a common mistake in your constructor and how you're calling the BMI calculation method. Let's walk through it step-by-step.
🔍 1. Problem in Constructor
In your Person constructor:
public Person(String userFirstName, double userHeightInches, double userWeightPounds) {
this.firstName = firstName;
this.heightInches = heightInches;
this.weightPounds = weightPounds;
}
You're using the wrong variable names inside the constructor. Instead of using userFirstName, userHeightInches, and userWeightPounds, you're using firstName, heightInches, and weightPounds which are the class fields. As a result, you're assigning null and 0.0 values to your object fields.
✅ Fix it like this:
public Person(String userFirstName, double userHeightInches, double userWeightPounds) {
this.firstName = userFirstName;
this.heightInches = userHeightInches;
this.weightPounds = userWeightPounds;
}
🔍 2. Incorrect BMI Calculation Call
In your displayBMI() method, you're passing 0 for both height and weight:
double userWeightPounds = 0;
double userHeightInches = 0;
double BMI = anyPerson.calculateBMI(userWeightPounds, userHeightInches);
So you're calling the calculateBMI() method with zeros, even though the anyPerson object already has the correct height and weight.
✅ You have two options to fix this:
Option 1: Change calculateBMI() to use object fields:
Update the Person class method to:
public double calculateBMI() {
return (this.weightPounds / (this.heightInches * this.heightInches)) * 703;
}
And then call it in displayBMI() like this:
double BMI = anyPerson.calculateBMI();
Option 2: Keep method parameters but pass actual values:
double userWeightPounds = anyPerson.getWeightPounds();
double userHeightInches = anyPerson.getHeightInches();
double BMI = anyPerson.calculateBMI(userHeightInches, userWeightPounds);
But Option 1 is cleaner and more object-oriented.
✅ Full Minimal Fixes Summary
Fix constructor variable names.
Use the actual object values to calculate BMI.
Optionally, update calculateBMI() to not require parameters.
🧪 Bonus Fix: Add BMI to the toString()
If you want to include BMI in the output string, modify your toString() like this:
@Override
public String toString() {
double bmi = calculateBMI();
return this.firstName + " weighs " + this.weightPounds + " lbs and is " + this.heightInches +
" inches tall. Your BMI is " + String.format("%.2f", bmi);
}
✅ Final Output Example:
Input:
John
70
150
Output:
John weighs 150.0 lbs and is 70.0 inches tall. Your BMI is 21.52
Healthy
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