invalid method declaration; return type required

[kelvin cheung]

 public void actionPerformed(ActionEvent klikk)
    {
        if (klikk.getSource() == btnMaks)
        {
            String f = txtFilnavn.getText();
            finnMaks(f);
        }
    }
    
    public static void main(String arg[])
    {
        GUI app = new GUI();
    }
    
    public finnMaks(String filnavn)
    {
       // String filnavn = "C:\\Documents and Settings\\wah\\Desktop\\temperatur.txt";
        
    try
    {
        
        FileReader leseforbindelse = new FileReader(filnavn); // forbindelse
        BufferedReader fil = new BufferedReader(leseforbindelse); // format
        double maks = 0;
        
        // read a line
        String enLinje = fil.readLine(); 
        
        while (enLinje != null)
        {
           // 1st is a year
           String year = enLinje; 
           
           System.out.print("year: " + year + " ");
           
           // read a line
           enLinje = fil.readLine(); 
           
           // 2nd is a temperature
           String temp = enLinje; 
           System.out.println("temperature: " + temp);
           
           // "doubletemp" is "temp" in "double" format // converted
           double doubletemp = Double.parseDouble(temp);
           
           // find out the max temperature
           if (doubletemp > maks)
           {
               maks = doubletemp;
           }
           
           // read a line
           enLinje = fil.readLine(); 
        }
        fil.close();
        return maks;
    } // end try
    
    catch (FileNotFoundException e)
    {
        System.out.println(filnavn + " ikke funnet");
        return;
    }
        
    catch (IOException e)
    {
        System.out.println("IO-feil oppst�tt ved oppkobling av forbindelse til " + filnavn);
        return;
    }
        
    } // end finnMaks 

ERROR

invalid method declaration; return type required
public finnMaks(String filnavn)
^
1 error

what's wrong here?

[Lars Vegas]

you need to define a return type, otherwise you have a constructor.
something like "public double finnMaks(String filnavn)"

[Tobias Hess]

you need to define a return type,
otherwise you have a constructor.
Otherwise you have an error; the only place where a return type must be omitted is the constructor.

[kelvin cheung]

hm... but i get " missing return value "
on my CATCH exception,
when i write
"public double finnMaks(String filnavn)" ?

[Ernest Friedman-Hill]

Because every path out of the function has to return a value. Add a "return 0" to the catch, or, perhaps better, don't catch the exception, but let it propagate to tell the caller that no value could be returned.

[kelvin cheung]

thanks guys!
so far i have added "return 0;" on the catch.
and it works fine.
but i got another error when i write :

 public void actionPerformed(ActionEvent klikk)
    {
        if (klikk.getSource() == btnMaks)
        {
            String f = txtFilnavn.getText();
            finnMaks(f);
            String stringMaks = Double.parseDouble(maks);
            txtFilnavn.setText(stringMaks);
            
        }
    } 

error :

GUI.java [149:1] cannot resolve symbol
symbol : variable maks
location: class GUI
String stringMaks = Double.parseDouble(maks);
^
GUI.java [149:1] incompatible types
found : double
required: java.lang.String
String stringMaks = Double.parseDouble(maks);
^
2 errors

it says that it cannot resolve symbol?
but "maks" has been returned back..

[Tobias Hess]

it says that it cannot resolve symbol?
but "maks" has been returned back..
No, the value of maks has been returned, not maks itself. If you want to do something with that value, you have to store it like this:
double x = finnMaks(f);
There's another problem here:
String stringMaks = Double.parseDouble(maks);
Double.parseDouble() makes a double from a string, this is not what you want - you really want the opposite, and I'm not sure but it has to be something like this:
Double d = new Double(x);
String stringMaks = d.toString();
HTH
[ April 13, 2004: Message edited by: Tobias Hess ]

[kelvin cheung]

hi again and thank you.
it should be like this

 if (klikk.getSource() == btnMaks)
        {
            String f = txtFilnavn.getText();
            finnMaks(f);
            String stringMaks = "" + maks;
            txtFilnavn.setText(stringMaks);
            
        } 

any idea what i can do with the MAKS?
thanks

[kelvin cheung]

i think i've found out :

 class GUI extends JFrame //implements ActionListener
{
    double maks; 
.....................

[Layne Lund]

You have the right idea. However, you also need to initialize the value of maks:

String f = txtFilnavn.getText();
double maks = finnMaks(f);

I might suggest that you use a different variable name. This will help you understand that this maks is different than the maks that is declared in finnMaks.
Layne