Regular expression to check if the string contains only number and char.

regular_expression_number_and_char_only.java

// 문자열이 문자와 숫자로만 되어 있는지 확인
public static boolean checkNumberCharMixed(@NonNull String password) {

    Pattern p = Pattern.compile("^([0-9]+[a-zA-Z]+|[a-zA-Z]+[0-9]+)[0-9a-zA-Z]*$");

    return p.matcher(password).matches();

}