问使用子字符串java分隔数字

EN

package Seperator_checker;

import java.util.Scanner;

public class Seperator {

    public static void main(String[] args) {
        Scanner number=new Scanner(System.in);
        System.out.print("Please Enter Your Number: ");
        String user_number=number.next();
        if(user_number.length()> 3) {
            user_number=user_number.substring(0,user_number.length()-3) + "," + user_number.substring(0,1);
            System.out.println("________________________________________");
            System.out.println("Your Currency Number Is: "+ user_number);
        }

    }

}