Test if char is '0'-'9' [migrated]

Posted by Chris Okyen on Programmers See other posts from Programmers or by Chris Okyen
Published on 2012-09-26T05:28:02Z Indexed on 2012/09/26 9:51 UTC
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My Java code is

// if the first character is not 0-9
if(
   (((input.substring(0,0)).compareTo("1")) < 0 || (((input.substring(0,0)).compareTo("9")) < 0));
      {
          System.out.println("Error: The first digit of the temperature is not 1-9. Force Exiting Program. ");
           System.exit(1); // exit the program
     }

But it slips through even with input like '1123' or '912' or '222', and gives this error message. Whether I have it > 0 for first and < 0 for the second, or > 0 and > 0, or < 0 and < 0, or even < o and > 0... How come?

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