如何修复NumberFormatException？

Question

I know this error is caused by a number format exception but i don't know how to fix it. i'v tried to do a function to Check if the variable is a Number or String and here is my code

public boolean checkNumber(String x) {
   try{
       Integer.parseInt(x);
       return true;
   }catch(NumberFormatException ex){
       return false;
   }
}

and this is a function takes a parameter of format dd/mm/yyyy, split and store it in an array, then call the previous function to determine if all index are integer number or not.

public boolean CheckBirthDate(String birthdate){
    int B = 0;
    String Line = birthdate;
    String[] seprated = Line.split("/");
    if( checkNumber(seprated[0])  && checkNumber(seprated[1])  && checkNumber(seprated[2])) {
        B = 1;
    }
    if(seprated.length == 3 && Integer.parseInt(seprated[0]) <= 31  && Integer.parseInt(seprated[1]) <=   12 && Integer.parseInt(seprated[2]) >= 1950 &&  Integer.parseInt(seprated[2]) <= 2017 && B == 1){
        return true;
    }else{
        return false;
    }
}

Answer 1

Why not use a DateFormat?

String birthday = "25/05/1973";
SimpleDateFormat format = new SimpleDateFormat("dd/MM/yyyy");
try {
    Date date = format.parse(birthday);
    System.out.println("date = " + date);
}
catch (ParseException e) {
     //date was bad format
}

Result:

date = Fri May 25 00:00:00 CET 1973

Answer 2

This will work:

public boolean CheckBirthDate(String birthdate) {
    int B = 0;
    String Line = birthdate;
    String[] seprated = Line.split("/");
    if (checkNumber(seprated[0]) && checkNumber(seprated[1]) && checkNumber(seprated[2])) {
        B = 1;
    }
    if (B == 1 && seprated.length == 3 && Integer.parseInt(seprated[0]) <= 31 && Integer.parseInt(seprated[1]) <= 12
        && Integer.parseInt(seprated[2]) >= 1950 && Integer.parseInt(seprated[2]) <= 2017) {
        return true;
    } else {
        return false;
    }
}

The problem is, that you check if B == 1 at the end of the if-clause and not the beginning. Therefore java tries to parse the Integer, even though it hasn't verified that it is actually a number yet.

I would also use a boolean vor B instead of an int. But generally speaking SurfMan's solution is probably the best and prettiest

Answer 3

I would recommend to debug in order to figure out where the error ocurs.

Any way, the last conditional, I suggest you to change the order. You first check if strings are numbers, thats perfect, then you store the result in a variable, fine. The thing is that the way conditionals work could be the problem here. You check whether are numbers or not at the end, and should be done at the begining, like:

if (B == 1 && seprated.length == 3 && Integer.parseInt(seprated[0]) <= 31 && Integer.parseInt(seprated[1]) <= 12
        && Integer.parseInt(seprated[2]) >= 1950 && Integer.parseInt(seprated[2]) <= 2017) {
        return true;
    } else {
        return false;
    }

This way first checks the first conditional, and if it is false, it doesnt keep doing the other conditions because false & true is always false