How to make java detect input correctly?

Question

When I change the list option in the code below, java picks up my input and gives me an answer that is really weird. This is the code:

package tempconverter;
import javax.swing.*;
import java.awt.event.*;
import java.awt.FlowLayout;
import static java.lang.System.out;
public class TempConverter extends JFrame implements ActionListener {
        final static String[] inList = {"From Celsius", "From Fahrenheit", "From Kelvin"};
        static JFrame f = new JFrame();
        static JTextField enter = new JTextField(3);
        static JButton confirm = new JButton("Convert");
        static JList choose = new JList(inList);
    public static void main(String[] args) {
        confirm.addActionListener(new TempConverter());
        f.setLayout(new FlowLayout());
        f.setSize(300, 60);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(enter); 
        f.add(confirm);
        f.add(choose);
        f.setVisible(true);        
    }
    @Override
    public void actionPerformed (ActionEvent e) {
        Object choice = choose.getSelectedValue();
        double toConvert = Double.parseDouble(enter.getText());
        double inF, inK, inC;
        if (choice.equals("From Celsius")) {
            inF = toConvert * 1.8 + 32;
            inK = toConvert + 273.15;
            out.println("In degrees Fahrenheit, " + toConvert + " degrees Celsius would be " + inF + " degrees.");
            out.println("In degrees Kelvin, " + toConvert + " degrees Celsius would be " + inK + " degrees.");
        }
        if (choice.equals("From Fahrenheit")) {
            inC = toConvert - 32 / 1.8;
            inK = toConvert - 32 / 1.8 - 273.15;
            out.println("In degrees Celsius, " + toConvert + " degrees Fahrenheit would be " + inC + " degrees.");
            out.println("In degrees Kelvin, " + toConvert + " degrees Fahrenheit would be " + inK + " degrees.");
        }
        if (choice.equals("From Kelvin")) {
            inC = toConvert - 273.15;
            inF = inC + 1.8 + 32;
            out.println("In degrees Celsius, " + toConvert + " degrees Kelvin would be " + inC + " degrees.");
            out.println("In degrees Fahrenheit, " + toConvert + " degrees Kelvin would be " + inF + " degrees.");
        }
    }
}

How do I make java realise that I changed the list selection? An example I tested is that I set the selection to "From Fahrenheit" and typed 32, but it gave me 14.222222222222221 degrees Celsius and -258.92777777777775 degrees Kelvin.

possible duplicate of [Is Java "pass-by-reference" or "pass-by-value"?](http://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value) — Kyle Hale, Aug 10 '14 at 14:18

sujithvm · Answer 1 · 2014-08-10T10:36:47.187

2

It should be +273.15 instead of -273.15, and typo with *. Change mentioned in comment

if (choice.equals("From Fahrenheit")) {
    inC = toConvert - 32 / 1.8;            
    inK = toConvert - 32 / 1.8 + 273.15;
    // change here ............^......

    out.println("In degrees Celsius, " + toConvert
            + " degrees Fahrenheit would be " + inC + " degrees.");
    out.println("In degrees Kelvin, " + toConvert
            + " degrees Fahrenheit would be " + inK + " degrees.");
}

if (choice.equals("From Kelvin")) {
    inC = toConvert - 273.15;
    inF = inC * 1.8 + 32;
    // .......^.... change here

    out.println("In degrees Celsius, " + toConvert
            + " degrees Kelvin would be " + inC + " degrees.");
    out.println("In degrees Fahrenheit, " + toConvert
                + " degrees Kelvin would be " + inF + " degrees.");
}

edited Aug 10 '14 at 10:36

answered Aug 10 '14 at 10:21

sujithvm

2,351
3
15
16

Still doesn't have a difference. Should I change something else? – TessellatingPi Aug 10 '14 at 12:25
@TessellatingPi can you explain issue ? Output seems fine to me – sujithvm Aug 10 '14 at 12:32
Sorry resolved it I didn't put brackets to indicate what goes first based on order of operations – TessellatingPi Aug 10 '14 at 13:25
@TessellatingPi okay. Hope it helped :) – sujithvm Aug 10 '14 at 14:19

dhanushkac · Answer 2 · 2014-08-10T10:34:31.287

First you have wrong calculation here.

inF = inC + 1.8 + 32;
here is working code.
```
if (choice.equals("From Kelvin")) {
inC = toConvert - 273.15;
inF = (inC * 1.8) + 32;
out.println("In degrees Celsius, " + toConvert + " degrees Kelvin would be " + inC + " degrees.");
out.println("In degrees Fahrenheit, " + toConvert + " degrees Kelvin would be " + inF + " degrees.");
    }
```
if (choice.equals("From Fahrenheit")) { inC = toConvert - 32 / 1.8; inK = (toConvert - 32 / 1.8) + 273.15; out.println("In degrees Celsius, " + toConvert + " degrees Fahrenheit would be " + inC + " degrees."); out.println("In degrees Kelvin, " + toConvert + " degrees Fahrenheit would be " + inK + " degrees."); }

How to make java detect input correctly?

2 Answers2