Question

I am trying to test if my user submits sensible data , which is later formatted to integer.
Where is the problem with the switch statement? 🙂

void convert(String str)
{
    int i=0;
    String x=str.startsWith();
    switch (x) {
        case 1:
        case 2:
        case 3:
        case 4:
        case 5:
        case 6:
        case 7:
        case 8:
        case 9:
        case 0:
            int i = Integer.parseInt(str);
            break;
        default:
            System.out.println ("Should start with fixnumber");
    }
    System.out.println (i);
}

Answer 1

You’re switching on x which is a String – unless you’re using Java 7, you can’t use String in a Switch statement.

I expect the error is actually coming from str.startsWith(), where that method is expecting to take a String (which you’re checking what it starts with) and returns a boolean, which you can’t switch on either.

UPDATE Correcting your code to do what I think you’re trying to do:

void convert(String str)
{
    int i = 0;
    switch (str.charAt(0)) {
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
        case '0':
            i = Integer.parseInt(str);
            break;
        default:
            System.out.println ("Should start with fixnumber");
    }
    System.out.println (i);
}

Although the shorter way is just to do the Integer.parseInt call, and handling the NumberFormatException that may occur – then you don’t need to do the switch at all.

void convert(String str)
{
    try {
        int i = Integer.parseInt(str);
        System.out.println (i);
    } catch (NumberFormatException e) {
        System.out.println ("Should start with fixnumber");
    }
}

You need to either return i; and convert the method signature from void to int, or otherwise expose the data in i to make it worthwhile.