Throwing a custom NumberFormatException in Java

Question

I am trying to throw my own NumberFormatException when convrting a String month into an Integer. Not sure how to throw the exception. Any help would be appreciated. Do I need to add a try-catch before this part of the code? I already have one in another part of my code.

// sets the month as a string
mm = date.substring(0, (date.indexOf("/")));
// sets the day as a string
dd = date.substring((date.indexOf("/")) + 1, (date.lastIndexOf("/")));
// sets the year as a string
yyyy= date.substring((date.lastIndexOf("/"))+1, (date.length()));
// converts the month to an integer
intmm = Integer.parseInt(mm);
/*throw new NumberFormatException("The month entered, " + mm+ is invalid.");*/
// converts the day to an integer
intdd = Integer.parseInt(dd);
/* throw new NumberFormatException("The day entered, " + dd + " is invalid.");*/
// converts the year to an integer
intyyyy = Integer.parseInt(yyyy);
/*throw new NumberFormatException("The yearentered, " + yyyy + " is invalid.");*/

Clanton

What's happening with the code that you commented out? – Tega

@Tega I receive a unreachable statment for any code after the throw. – Clanton

I took out the throw statements and added my own String to where I was catching the exception earlier in my code. – Clanton

Answer 1

something like this:

try {
    intmm = Integer.parseInt(mm);
catch (NumberFormatException nfe) {
    throw new NumberFormatException("The month entered, " + mm+ " is invalid.");
}

Or, a little bit better:

try {
    intmm = Integer.parseInt(mm);
catch (NumberFormatException nfe) {
    throw new IllegalArgumentException("The month entered, " + mm+ " is invalid.", nfe);
}

EDIT: Now that you've updated your post, it seems like what you actually need is something like parse(String) of SimpleDateFormat

Eldoria

The second example is nice because it will chain together the exceptions, so you can see that the cause of the Illegal Args was the Number Format Exception. – Pya

@Eldoria I took out the throw statements and added my own String to where I was catching the exception earlier in my code. catch (NumberFormatException NFE) { System.out.println(NFE.getMessage() + " has non numeric input in entry");} Thanks for your input – Clanton

Answer 2

try {
   // converts the month to an integer
   intmm = Integer.parseInt(mm);
} catch (NumberFormatException e) {
  throw new NumberFormatException("The month entered, " + mm+ " is invalid.");
}

Sportswear

Yes, you are right because if raised a RuntimeException ... But in this context the probability are low. However you are right. – Sportswear

I took out the throw statements and added my own String to where I was catching the exception earlier in my code. catch (NumberFormatException NFE) { System.out.println(NFE.getMessage() + " has non numeric input in entry");} Thanks for your input! – Clanton

Answer 3

Integer.parseInt() already produces NumberFormatException. In you example it seems more appropriate to throw IllegalArgumentException:

int minMonth = 0;
int maxMonth = 11;
try 
{
    intmm = Integer.parseInt(mm);
    if (intmm < minMonth || intmm > maxMonth) 
    {
      throw new IllegalArgumentException
      (String.format("The month '%d' is outside %d-%d range.",intmm,minMonth,maxMonth));
    }
}
catch (NumberFormatException nfe) 
{
  throw new IllegalArgumentException
  (String.format("The month '%s'is invalid.",mm) nfe);
}

Involucre

I took out the throw statements and added my own String to where I was catching the exception earlier in my code. catch (NumberFormatException NFE) { System.out.println(NFE.getMessage() + " has non numeric input in entry");} Thanks for your input – Clanton