I'm look for some help on a bit of homework I have. I want the user to enter a numerical String, then convert it to an Integer. But I want to make a loop that will detect if the user entered in the wrong value such as "One Hundred" as apposed to "100".

What I was thinking was to do something like this:

 do{ numStr = JOptionPane.showInputDialog("Please enter a year in numarical form:" + "\n(Ex. 1995):"); num = Integer.parseInt(numStr); if(num!=Integer){ tryagainstr=JOptionPane.showInputDialog("Entered value is not acceptable." + "\nPress 1 to try again or Press 2 to exit."); tryagain=Integer.parseInt(tryagainstr); } else{ *Rest of the code...* } }while (tryagain==1);

But I don't know how to define that "Integer" value. I essentially want it to see if it is a number or not to prevent it from crashing if the user enters the wrong thing.

1

4 Answers

Try this:

 try{ Integer.valueOf(str); } catch (NumberFormatException e) { //not an integer }

Try use instanceof , this method will help you with check between many types

Example

if (s instanceof String ){
// s is String
}else if(s instanceof Integer){
// s is Integer value
}

If you want just check between integer and string you can use @NKukhar code

try{ Integer.valueOf(str); } catch (NumberFormatException e) { //not an integer }

try this

int num;
String s = JOptionPane.showInputDialog("Enter a number please");
while(true)
{ if(s==null) break; // if you press cancel it will exit try { num=Integer.parseInt(s); break; } catch(NumberFormatException ex) { s = JOptionPane.showInputDialog("Not a number , Try Again"); }
}

1

Use a regex to validate the format of the string, and accept only numeric values on it:

Pattern.matches("/^\d+$/", numStr)

The matches method will return true if numString contains a valid numeric sequence, but of course the input can be way above an Integer's capacity. In that case, you can consider switching to a long or a BigInteger type.

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