• April 27th, 2010, 01:14 PM
Umogrim
Hello all, I am new to this forum, and also to java, so bear with me a bit.
I got this exercise in lab class to make a program that converts from one type of temperature to the other two(eg. Celsius to farenheit and kelvin). Now, I was progressing along nicely, and managed to make the first one(for Celsius) work, however Farenheit and Kelvin converters don't work. I asked my lab helper what was wrong, and he was stumped. The IDE(netbeans 6.8) isn't showing any underlined red errors, so I hope someone here could help me.

Code :

```import java.io.*;   public class Main {   public static void main(String[] args) throws IOException { BufferedReader bf=new BufferedReader(new InputStreamReader(System.in)); System.out.println("Ingrese la medida de temperature que quiere convertir(1: Celsius, 2: Farenheit, 3:Kelvin): ");   if(1==Integer.parseInt(bf.readLine())) { new BufferedReader(new InputStreamReader(System.in)); System.out.print("Ingrese la temperatura Celsius que quiere convertir: "); double c=Double.parseDouble(bf.readLine());   double kelvinC = c + 273.15; double farenheitC = 1.8*c + 32;   System.out.print("La temperatura "+c+"°C es equivalente a "+farenheitC+"°F y "+kelvinC+"°K."); }   if(2==Integer.parseInt(bf.readLine())) { new BufferedReader(new InputStreamReader(System.in)); System.out.println("Ingrese la temperatura Farenheit que quiere convertir: "); double f=Double.parseDouble(bf.readLine());   double celsiusF=(f-32)/1.8; double kelvinF=(f+459.67)/1.8;   System.out.print("La temperatura "+f+"°F es equivalente a "+celsiusF+"°C y "+kelvinF+"°K."); }   else if(3==Integer.parseInt(bf.readLine())) { new BufferedReader(new InputStreamReader(System.in)); System.out.println("Ingrese la temperatura Kelvin que quiere convertir: "); double k=Double.parseDouble(bf.readLine());   double celsiusK=k-273.15; double farenheitK=(9/5)*k - 459.67;   System.out.print("La temperatura "+k+"°K es equivalente a "+celsiusK+"°C y "+farenheitK+"°F"); }     }   }```

When it prompts me with "Ingrese la medida de temperature que quiere convertir(1: Celsius, 2: Farenheit, 3:Kelvin): ", any answer other than 1 gives me this error:

Exception in thread "main" java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(Num berFormatException.java:48)
at java.lang.Integer.parseInt(Integer.java:470)
at java.lang.Integer.parseInt(Integer.java:499)
at laboratorio1.Main.main(Main.java:32)
Java Result: 1
BUILD SUCCESSFUL (total time: 14 seconds)

I hope someone can help me, thanks in advance.
• April 28th, 2010, 08:58 AM
JavaPF
I have compiled your code but I do not get this error when I enter anything other than 1. I can clearly see it doesn't work though.

I don't really think the way you have coded this is the best method..

I will post an update shortly.
• April 28th, 2010, 09:12 AM
JavaPF
Try this :D

Code :

```import java.io.*;   public class Main {   public static void main(String[] args) throws IOException { BufferedReader bf=new BufferedReader(new InputStreamReader(System.in));   System.out.println("Ingrese la medida de temperature que quiere convertir(1: Celsius, 2: Farenheit, 3:Kelvin): ");   String myString = bf.readLine();   if(myString.equals("1")) { new BufferedReader(new InputStreamReader(System.in)); System.out.print("Ingrese la temperatura Celsius que quiere convertir: "); double c=Double.parseDouble(bf.readLine());   double kelvinC = c + 273.15; double farenheitC = 1.8*c + 32;   System.out.print("La temperatura "+c+"°C es equivalente a "+farenheitC+"°F y "+kelvinC+"°K."); }   else if(myString.equals("2")) { new BufferedReader(new InputStreamReader(System.in)); System.out.println("Ingrese la temperatura Farenheit que quiere convertir: "); double f=Double.parseDouble(bf.readLine());   double celsiusF=(f-32)/1.8; double kelvinF=(f+459.67)/1.8;   System.out.print("La temperatura "+f+"°F es equivalente a "+celsiusF+"°C y "+kelvinF+"°K."); }   else if(myString.equals("3")) { new BufferedReader(new InputStreamReader(System.in)); System.out.println("Ingrese la temperatura Kelvin que quiere convertir: "); double k=Double.parseDouble(bf.readLine());   double celsiusK=k-273.15; double farenheitK=(9/5)*k - 459.67;   System.out.print("La temperatura "+k+"°K es equivalente a "+celsiusK+"°C y "+farenheitK+"°F"); }     }   }```
• April 28th, 2010, 09:16 AM
copeg
If you press enter and read an empty line you will receive a NumberFormatException. Your program won't respond for 2 or 3 because you read the line upon checking for 1, if it is not one the program waits to read the next line. You should read the line first, then check the value:

Code :

```String line = br.readLine(); if(1==Integer.parseInt(line))```
Ideally, you would also have a way to validate the user entries rather than having your program exit with an exception.

EDIT: Doh! JavaPF beat me to the punch with a much more thorough response
• April 28th, 2010, 04:47 PM
JavaPF
Quote:

Originally Posted by copeg
If you press enter and read an empty line you will receive a NumberFormatException. Your program won't respond for 2 or 3 because you read the line upon checking for 1, if it is not one the program waits to read the next line. You should read the line first, then check the value:

Code :

```String line = br.readLine(); if(1==Integer.parseInt(line))```
Ideally, you would also have a way to validate the user entries rather than having your program exit with an exception.

EDIT: Doh! JavaPF beat me to the punch with a much more thorough response

=:) Good work copeg.
• April 28th, 2010, 08:51 PM
copeg