java.lang.NumberFormatException：对于输入字符串：使用“ 2”或“ 5”时为“”

Question

I read in a menu choice and typing in any number but 2 & 5 work.

String choice = promptUser(choicePrompt);
try {
      outputInfo(String.format("choice=...%s...",choice));
      int c = Integer.parseInt(choice);
      /* process it */
}catch (NumberFormatException e) {

outputInfo(String.format("choice=%s",choice));
outputInfo(e.toString());
}

public static void outputInfo(String msg)
{
    System.out.printf("\t%s\n",msg);
}

Good output:

    Enter Option: 1
    choice=...1...

Bad Output:

    Enter Option: 2
    choice=...2...
    choice=2
    java.lang.NumberFormatException: For input string: ""

Update:

I've hard-coded "2" and it still fails!:

String choice = promptUser(choicePrompt);
try {
     choice="2";
     outputInfo(String.format("choice=...%s...",choice));
     int c = Integer.parseInt(choice);
     /* process it */
}catch (NumberFormatException e) {

outputInfo(String.format("choice=%s",choice));
outputInfo(e.toString());
}

Hard-coding "5" also fails but "1" works!!!

Any ideas gratefully received.

Simon

Answer 1

If I assume your promptUser() method to be something like:

static String promptUser() {
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    try {
        return reader.readLine();
    }
    catch(Exception ex) {
        return null;
    }
}

(without the parameter) then the program behaves as expected - certainly there's nothing in that code that treats 2 or 5 differently. If you're getting an empty string then are you sure your prompt user method is working correctly?

Either way, the code you've posted here is essentially correct. I would imagine there's something else wrong in your more fully complete program that doesn't manifest itself when you've reduced it down here; perhaps you're running into a case where a local variable is hiding a field for example and you're not using the value you think you are (but at this point, I'm just guessing.)

Answer 2

updated

Seems the promptUser method is returning an empty String "". check if choice is empty before calling ParseInt method

Also you can add trim() to eliminate spaces before and after the input

  if(choice!=null && !"".equals(choice))
     int c = Integer.parseInt(choice.trim());

Answer 3

printStackTrace() is your friend. Turns out the number format exception was further down (in the 'process it' code) and was not being caught down there. It was data driven so didn't happen on other machines.

Thanks to every one for your support.

Simon