java textbook exercise

[feartrich]

This supposed to return the user's BMI. But the output is always 0. Why is that?

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.DecimalFormat;

public class bmi extends JApplet
  implements ActionListener
{
  JTextField inputLbs, inputInches, displayBmi;

  public void init()
  {
    JLabel labelLbs = new JLabel("Weight (lbs):", SwingConstants.RIGHT);
    inputLbs = new JTextField(5);
    JLabel labelInches = new JLabel("Height (inches):", SwingConstants.RIGHT);
    inputInches = new JTextField(5);
    JLabel labelBmi = new JLabel("BMI = ", SwingConstants.RIGHT);
    displayBmi = new JTextField(5);
    displayBmi.setEditable(false);
    JButton go = new JButton("Compute");
    go.addActionListener(this);

    Container c = getContentPane();
    c.setBackground(Color.white);
    JPanel p = new JPanel();
    p.setLayout(new GridLayout(3, 2, 5, 5));
    p.add(labelLbs);
    p.add(inputLbs);
    p.add(labelInches);
    p.add(inputInches);
    p.add(labelBmi);
    p.add(displayBmi);
    c.add(p, BorderLayout.CENTER);
    c.add(go, BorderLayout.SOUTH);
  }

  public void actionPerformed(ActionEvent e)
  {
    int lbs = Integer.parseInt(inputLbs.getText());
    int inches = Integer.parseInt(inputInches.getText());
    double bmi = calculateBmi(lbs, inches);
    DecimalFormat df = new DecimalFormat("00.0");
    displayBmi.setText(df.format(bmi));
  }

  private double calculateBmi(int lbs, int inches)
  {
    return (lbs * 2.2) / ((inches * 39.4)*(inches * 39.4));
  }
}

[VernonDozier]

This supposed to return the user's BMI. But the output is always 0. Why is that?

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.DecimalFormat;

public class bmi extends JApplet
  implements ActionListener
{
  JTextField inputLbs, inputInches, displayBmi;

  public void init()
  {
    JLabel labelLbs = new JLabel("Weight (lbs):", SwingConstants.RIGHT);
    inputLbs = new JTextField(5);
    JLabel labelInches = new JLabel("Height (inches):", SwingConstants.RIGHT);
    inputInches = new JTextField(5);
    JLabel labelBmi = new JLabel("BMI = ", SwingConstants.RIGHT);
    displayBmi = new JTextField(5);
    displayBmi.setEditable(false);
    JButton go = new JButton("Compute");
    go.addActionListener(this);

    Container c = getContentPane();
    c.setBackground(Color.white);
    JPanel p = new JPanel();
    p.setLayout(new GridLayout(3, 2, 5, 5));
    p.add(labelLbs);
    p.add(inputLbs);
    p.add(labelInches);
    p.add(inputInches);
    p.add(labelBmi);
    p.add(displayBmi);
    c.add(p, BorderLayout.CENTER);
    c.add(go, BorderLayout.SOUTH);
  }

  public void actionPerformed(ActionEvent e)
  {
    int lbs = Integer.parseInt(inputLbs.getText());
    int inches = Integer.parseInt(inputInches.getText());
    double bmi = calculateBmi(lbs, inches);
    DecimalFormat df = new DecimalFormat("00.0");
    displayBmi.setText(df.format(bmi));
  }

  private double calculateBmi(int lbs, int inches)
  {
    return (lbs * 2.2) / ((inches * 39.4)*(inches * 39.4));
  }
}

It isn't always 0. But it's extremely low and the fact that you're only allowing one decimal precision causes everything to round down to 0. Any normal person (i.e. 6 ft. tall, 200 lbs.) is going to have a very small BMI by your formula. Have a 6 ft. man weigh one million pounds and you'll get a non-zero answer (but even then it'll only be 0.3). You have a problem in your formula:

return (lbs * 2.2) / ((inches * 39.4)*(inches * 39.4));