請使用者輸入密碼，並檢測密碼是否有效
有效條件：

• 密碼必須至少八位字元
• 密碼僅能包含字母和數字

• 密碼必須包含至少兩個數字

  小結：正則表示式檢驗字串

package test;
import java.util.Scanner;
public class passwordDetection {
    public static void main(String[] args) {
        String password = "";
        do {
        password = getPassword();
        }while(rule(password) == false
 
);
    }

    /*獲取密碼*/
    public static String getPassword() {
        Scanner input = new Scanner(System.in);
        System.out.println("請輸入密碼：");
        String password = input.nextLine();
        return password;
    }

    /*檢驗密碼*/
    public static boolean rule(String password) {
        if(eightWord(password) == false
 
) {
            System.out.println("您輸入的不是八位！");
            return false;
        }
        else if (numberWord(password) == false) {
            System.out.println("您輸入的密碼應僅包含數字和字母！");
            return false;
        }
        else if (twoNumber(password) == false) {
            System.out.println("密碼應至少兩個數字！"
 
);
            return false;
        }
        else {
            System.out.println("密碼合格！");
            return true;
        }
    }

    /*檢驗至少八位密碼*/
    public static boolean eightWord (String password) {
        int len = password.length();
        if (len >= 8)
            return true;
        else
            return false;
    }

    /*檢驗密碼僅能包含字母和數字*/
    public static boolean numberWord (String password) {
        boolean flag = password.matches("[a-zA-Z0-9]{8,}");
        return flag;
    }

    /*檢驗密碼包含至少兩個數字*/
    public static boolean twoNumber (String password) {
        char word;
        int i = 0,flag = 0;
        for(i = 0; i < 8; i++) {
            word = password.charAt(i);
            if(word < '9' && word > '0')
                flag++;
            if(flag >= 2)
                return true;
        }
        return false;
    }
}