检查字符串在数字范围内Java

Question

Trying to design a simple lottery program. Everything works except checking if the numbers entered are between 1 to 59.

Exercise says the numbers must be stored in a String variable.

so

if(num<0 || num>59) //wont work for me

Tried making another variable

int numConverted = Integer.parseInt(num)

We haven't covered converting String to int in class though so I don't think this is what expected. Got confused trying that way anyway so probably this is wrong.

Here is the code I have currently.

{
    Scanner scan = new Scanner(System.in);

    String num=""; //num variable is empty untill user inputs numbers

    for(int i =0; i<6; i++) 
    {
        System.out.println("Enter your number between 1-59");
        num = num +" "+ scan.nextLine(); 
    }

    System.out.println("Ticket printed £2. Your numbers are " + num);
}

Answer 1

In your posted code it's obvious that you want the User to supply 6 specific numerical values. These values are appended to the String variable named num (space delimited). You need to obviously do a few things here:

1) Make sure the value supplied by the user is indeed a numerical value;

2) Make sure the numerical values supplied fall within the minimum and maximum scope of the lottery itself (which you have stated is: 1 to 59);

3) Make sure the number entered by the User hasn't been supplied already.

You've been tasked to store the entered values into a String data type variable and that is all fine but at some point you want to carry out value comparisons to make sure that all the entered values actually play within the limits of the lottery.

When the User completes his/her entries, you end up with a space delimited string held in the num string variable. You now need to make sure that these values entered are indeed....numbers from 1 to 59 and none contain alpha characters.

In my opinion (and this is only because you need to store entered values into a String variable), it's best to use your String variable to gather User input, then test the input to make sure it is indeed a string representation of an actual integer number. Once this is established then we test to make sure if falls within the value min/max limits (1-59). Now we need to test to make sure the number entered hasn't already been entered before for this ticket.

Of course with each test described above, if one fails then the User should be prompted to re-enter a proper value. You can do this by utilizing a while loop. Plenty examples of this in StackOverflow but here's a quick example:

Scanner scan = new Scanner(System.in);
String ticketNumbers = "";
for(int i = 0; i < 6; i++) {
    Boolean isOK = false;
    while (!isOK) {
        System.out.println("\nPlease enter your desired 6 ticket numbers:\n"
                + "(from 1 to 59 only)");
        String num = scan.nextLine(); 
        //Is the string entered an actual integer number?
        //We use the String.matches() method for this with
        //a regular expression.
        if(!num.matches("\\d+")) {
            System.out.println("You must supply a numerical value! "
                    + "Try Again...");
            continue;
        }
        if (ticketNumbers.contains(num + " ")) {
            System.out.println("The number you supplied has already been chosen!"
                    + " Try Again...");
            continue;
        }
        if (Integer.parseInt(num) >= 1 && Integer.parseInt(num) <= 59) {
            ticketNumbers+= num + " ";
            isOK = true;
        }
        else {
            System.out.println("The number you supply must be from "
                    + "1 to 59! Try Again...");
        }
    }
}
System.out.println("Ticket printed £2. Your numbers are " + ticketNumbers);

Answer 2

How about -

if(Integer.parseInt(num) < 0 || Integer.parseInt(num) > 59)

This should work, place it after the input.

If it works, please mark this as correct, I need the rep!!!

Answer 3

Easy way would be add available numbers (suppose it wont grow more than 60. You can use a loop to add to this as well)

String numbers[] = {"1","2","3", "..."};

Then inside the loop

 Arrays.asList(numbers).contains(num);

You can remove prefixing zero in order avoid conflicts with values like '02'

Here everything is String related.

Answer 4

If you don't want to explicitly convert to int , you could use a regular expression.

if (num.matches("[1-5]?[0-9]")) {
    ...

This checks whether the String consists of (1) maybe a digit from 1 to 5, followed by (2) definitely a digit from 0 to 9. That'll match any number in the range 0-59.

If you've got a whole series of numbers separated by spaces, you could expand this to cover a whole series like this.

if (num.matches("([1-5]?[0-9]\\s+)*[1-5]?[0-9]")) {

This matches any number of repetitions (including zero) of "a number followed by spaces", followed by a single repetition without a space. The "\\\\s" means "any whitespace character", the "+" after it means "one or more of what precedes", and the "*" means "zero more of what precedes" - which in this case is the term in parentheses.

Answer 5

Oh I see what you are trying to do

This is what you want

    Scanner scan = new Scanner(System.in);


String allNums = "";


for(int i =0; i<6; i++) 
{
    System.out.println("Enter your number between 1-59");
    int num = scan.nextInt();//Take the number in as an int 

    if(num >0 && num < 59)//Check if it is in range
    {
        allNums += num + " ";//if it is add it to a string
    }
    else
    {
        System.out.println("Number not in range");
        i--;//go back one iteration if its not in range
    }


}

System.out.println("Ticket printed £2. Your numbers are " + allNums);