我的代码中出现运行时错误。当我输入字母时，布尔有效值变为true

Question

该代码将输入密码，并检查密码是否包含字母和数字。如果没有密码，则两个注册都将继续。当我输入字母和数字时，寄存器是完整的；当我输入数字时，只有寄存器会继续；当我输入字母时，只有寄存器是完整的而不包含数字。import java.io.*;public class Sample {static BufferedReader dataIn = new BufferedReader(new InputStreamReader(System.in));public static void main (String[] args)throws Exception {    boolean valid = false;    boolean alphaCheck = false;    boolean numCheck = false;    char[] alpha = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};    char[] num = {'1', '2', '3', '4', '5', '6', '7', '8', '9', '0'};    do {        System.out.println("Password must contain Letters and Numbers Only. (abc../ABC.., 123..)");        System.out.println("Special Characters are not Allowed.");        System.out.print("Register Password: ");        String password = dataIn.readLine();        char[] passwordToArray = password.toUpperCase().toCharArray();        // Check if password contains numbers        for(char x: passwordToArray){            for(char y: num){                if(x==y){                    numCheck = true;                    break;                }            }        }        // Check if password contains Letters        for(char x: passwordToArray){            for(char y: alpha){                if(x==y){                    alphaCheck = true;                    break;                }            }        }        if(!numCheck){            System.out.println("No Numbers Found.");        }        if(!alphaCheck){            System.out.println("No Letters Found.");        }        // Check if password contains both Alphabets and Numbers        // if false Continue Register        if((numCheck)&&(alphaCheck)){            System.out.println("Register Complete");            valid = true;        }else{            System.out.println("Register Failed. Please Try again");        }    }while (!valid) ;}}