在 do while 循环中正确使用 Scanner.next(Pattern pattern) 的问题

Question

I have a menu where integers zero through six have different actions. If one the user input is proper, it performs the action successfully and asks for input again for the next action to perform. To exit the program menu, the user input must be six. If any invalid input is received, it prints "invalid option" and reprints asks for input again. My code I have is:

int menuSelection;
Scanner reader = new Scanner(System.in);  // Reading from System.in

do
{
    System.out.println("Enter a number: ");
    if (reader.hasNext(Pattern.compile("^[0-6]$")))
    {
        menuSelection = reader.nextInt();
    }
    else
    {
        System.out.println("Invalid option");
        reader.next();
    }
} while(menuSelection != 6);
//once finished
reader.close();

The output I have is:

Enter a number: 
1
Enter a number: 
2
Invalid option
Enter a number: 
3
Invalid option
Enter a number: 
4
Invalid option
Enter a number: 
5
Invalid option
Enter a number: 
6
Invalid option
Enter a number: 
7
Invalid option
Enter a number: 
8
Invalid option
Enter a number: 
pancake
Invalid option
Enter a number: 

So it's properly handling the first ever input I give it, but after that, it's stuck in an infinite loop because it always thinks my input is incorrect. My logic here was to have a do while that always repeats as long as menuSelection is not 6, because that's the only time the program will ever exit, everything else should loop back to waiting for input. So then inside the do while loop I was hoping I can error check there, making sure that the input is within the bounds of 0-6 and also strictly integer type, otherwise to go through the loop again without performing the action (which isn't actually coded into the if block yet).

I'm pretty new to Java, so I'm not the most familiar with Scanner and how it handles validation. I guess my question is, what is causing my other inputs to be invalid?

Answer 1

Check your RegEx. Try:

if (reader.hasNext(Pattern.compile("[0-6]"))) {
    menuSelection = reader.nextInt();
}

This means, when the pattern [0-6] ( any number between 0 and 6 ) was detected then it works as you expected it to.

[edit]

I removed the {1} ( only one time ) at the end, as cricket_007 proposed.

[/edit]

Example:

Enter a number: 
sdf
Invalid option
Enter a number: 
3
Enter a number: 
2
Enter a number: 
1
Enter a number: 
5
Enter a number: 
8
Invalid option
Enter a number: 
6