Question

Im writing a program for homework where I need to validate user input and then create an object and add it to an array list. i have included just what i think is the relevant code, but im a beginner for sure so let me know if there is something else you need to see.

I have the user enter a string, then check to see if its a double. if its not a double, i throw an exception that i created

     try{
        price = Double.parseDouble(strPrice);
     }
     catch(NumberFormatException nfe){
        CDException cde = new CDException();
        cde.setMessage("Price must be a number,\nCannot create CD");
        throw cde;
     }

after making sure that it is a number, in my other class i check to make sure it is in the range that i want. (non negative in this case) then create an object with the value

public void setPrice(double newPrice)throws Exception{
    if(newPrice >= 0){
        this.price = newPrice;
    }
    else{
        CDException cde = new CDException();
        cde.setMessage("CD Price cannot be negative,\nCannot create CD");
        throw cde;
    }
}

so my question is…

is there a way to do this in one step, check both that the user entered a number and that the number is non negative. one other thing is that if the input is blank, that is the instruction to end the input loop.

Answer 1

Well, you could change your code to read:

try {
    price = Double.parseDouble(strPrice);
    if (price < 0) {
        throw new CDException("Can't be negative");
    }
} catch (NumberFormatException ex) {
     ...
}

But the question is whether you’d really like to do that. From a design perspective, it might make more sense to do the “negative” check inside setPrice, rather than doing it as part of the parsing logic.