Help: Getting this error: Error:(3, 41) java: <identifier> expected

[Khayla Matthews]

Hello and thanks in advance for your time,

I am getting this error 'Error:(3, 41) java: <identifier> expected' on a really simple program. Why won't this code run?

public class absvalprob {
    double a = 5;
    public double absoluteValue(a){
            if (a<0){
                return -a;
            }else{
                return a;
            }
        }
    }

[Junilu Lacar]

on Line 3, the parameter a has no declared type. Specify what its type is. I'd guess you want that to be a double.

[Khayla Matthews]

Oh, I thought that wasn't necessary since I just declared the variable. But, now I'm getting this error
Error: Main method not found in class absvalprob, please define the main method as:
  public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application.

Do I need to put a main method before my own functions?

[Junilu Lacar]

It doesn't matter where you add the main() method. You do need it if you're going to run this code with "java absvalprob" though.

By convention, class names should start with a capital letter and use camelcase for other words. So your class name should be AbsvalProb instead.

[Junilu Lacar]

Khayla Matthews wrote:Oh, I thought that wasn't necessary since I just declared the variable. But, now I'm getting this error

The a that you declared on line 2 is not the same as the a you specify as a parameter to that method. Those are two entirely different things.

[Khayla Matthews]

So, I'm still a little confused. I changed my code to the following and I'm still getting errors. What am I doing wrong? Thanks again for your help.

public class AbsValProb {
    double a = 5;
    double value;

    public static void main(String[] args) {
        public double absoluteValue ( double a){
            if (a < 0) {
                value = -a;
            } else {
                value = a;
            }
            return value;
        }
    }
}

[Junilu Lacar]

You put the absoluteValue() method inside the main() method. You can't do that.

[Khayla Matthews]

Got it. No more errors! Thanks again.

[Junilu Lacar]

The main() method needs to have code that does something. You probably want to call the absoluteValue() method from the main() method and display its result.

Here's an example:

public class Demo {

    public static void main(String[] args) {
        System.out.println("The sum of 1 and 2 is " + sum(1, 2)); 
    }

    public static int sum(int n1, int n2) {
        return n1 + n2;
    }
}

[Campbell Ritchie]

If you find the old Sun style guide, it tells you to avoid if (something) return someValue; else return differentValue;I would write that absValProb method like this:-

public static double absoluteValue(double x)
{
   return x < 0 ? -x : x;
}

Please find out what happens if you pass NaN as an argument.

[Khayla Matthews]

I rewrote the code to look like so and it runs perfectly with no errors. The format recommended by the style guide takes some getting used to but I think I like it better.

public class AbsValProb {
        public static void main(String[] args){
            System.out.println("The absolute value is "+ absoluteValue(2.0)) ;
        }
        public static double absoluteValue (double value){
            return (value > 0?value:-value);
        }
    }

[Khayla Matthews]

Campbell Ritchie wrote:If you find the old Sun style guide, it tells you to avoid if (something) return someValue; else return differentValue;I would write that absValProb method like this:-

public static double absoluteValue(double x)
{
   return x < 0 ? -x : x;
}

Please find out what happens if you pass NaN as an argument.

<br /> <br /> Not sure what you mean by passing NaN as an argument. I would like to see what happens though. I updated my code like so, and got a ton of erros. so I think I did it wrong. <br /> <br />

public class AbsValProb {
        public static void main(String[] args){
            System.out.println("The absolute value is "+ absoluteValue(2.0)) ;
        }
        public static double absoluteValue (double NaN){
            return (value > 0?value:-value);
        }
    }

[Ron McLeod]

Khayla Matthews wrote:Not sure what you mean by passing NaN as an argument

He probably means something like: absoluteValue(Double.NaN)

[Campbell Ritchie]

Ron McLeod wrote:. . . He probably means something like: . . .

Yes, I did.
Or absoluteValue(0.0 / 0.0)
Or absoluteValue(Math.log(-1.0))
Or absoluteValue(Math.sqrt(-1.0))
They will all end up sending NaN as an argument.