package com.mathlearning.util;

public class UsernameValidator {
    public static boolean isValid(String username) {
        if (username == null || username.length() < 3 || username.length() > 20) {
            return false;
        }
        
        return username.matches("^[a-zA-Z0-9_]+$");
    }
    
    public static String getRequirements() {
        return "用户名要求: 3-20位，只能包含字母、数字和下划线";
    }
}