如何在以下代码中使用循环，以便如果用户再次输入任何字母程序时要求输入数字而不是终止程序？

Question

如何应用循环，以便当用户输入任何字母程序时，它会提示用户再次输入数字而不是终止程序？

public class prac{
    public static void main(String[] args) throws FileNotFoundException{
        Scanner in = new Scanner(System.in);
        System.out.println("Enter your Cell Phone number : ");
        double phonenumber;

        phonenumber = in.nextDouble();                                
    }
}

Answer 1

按照下面的方法做

Pattern pattern = Pattern.compile("^[0-9]+$");
Scanner in = new Scanner(System.in);
double phonenumber = 0;
String input;
Matcher matcher;
boolean stop=false;

while (!stop) {
     System.out.println("Enter your Cell Phone number : ");
     input = in.nextLine();  
     matcher = pattern.matcher(input);
     if (matcher.find()) {
           stop=true;
           phonenumber=Double.parseDouble(input);
     }          
}

System.out.println("User phone number is "+phonenumber);

编辑：

^        match the beginning of the line
[0-9]    match a digit 
+        match 1 or more times
$        match the end of the line