密碼驗證程序Java

Question

我目前正在研究我的Java類的最終項目，我需要一點幫助！所以首先我要告訴你的指示，我的代碼，然後是我的問題。

說明

1. 編寫提示用戶輸入密碼的程序。
2. 創建一個名爲valid的布爾變量並將其設置爲true。如果以下任何測試失敗，請將其設置爲true。
3. 檢查密碼，看它是否至少有8個字符。如果沒有，則顯示消息「密碼必須至少包含8個字符」

4. 檢查密碼以查看它是否僅包含字母和數字。爲此，您需要遍歷字符串中的所有字符。角色C是數字信如果此表達式爲真：

   （ 'A' < = C & &Ç< = 'Z'）|| （'A'< = c & & c < ='Z'）|| （ '0' < = C & &Ç< = '9'）

，如果這是即使不是真的，從你的循環打破並顯示信息， 「密碼必須只包含字母和數字」 5.如果程序結束時仍然有效，請顯示消息「密碼已接受！」。

我的代碼

import java.util.Scanner; 
public class PasswordVerification { 

    public static void main(String[] args) { 
//  Creates a scanner 
     Scanner sc = new Scanner(System.in); 
     boolean valid = false; 
     String password; 


//  Asks user to enter password 
     System.out.print("Please enter password and then hit enter:"); 
     password = sc.nextLine(); 

//  Checks to see if password is at least 8 characters. 
     if (password.length()<8) 
      { 
       valid = false; 
       System.out.println("Password must have at least 8 characters"); 
      } 

//  Checks each character to see if it is acceptable. 
     for (int i = 0; i < password.length(); i++){ 
        char c = password.charAt(i); 

        if (  ('a' <= c && c <= 'z') // Checks if it is a lower case letter 
          || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter 
          || ('0' <= c && c <= '9') //Checks to see if it is a digit 
        ) 
        { 

         valid = true; 
        } 

        else 
        { 
         // tells the user that only letters & digits are allowed 
         System.out.println("Only letter & digits are acceptable."); 
         valid = false; 
         break; 
        } 

     } 

     // if the password is valid, tell the user it's accepted 
     System.out.println("Password Accepted"); 
     } 


} 

因此，有說明書和我的代碼，我到目前爲止。我接近完成我只是在第四部分遇到問題。因此，預期輸出應該是：

Please enter a password: abc 
Password much have at least 8 characters 
Please enter a password: abcd1234$ 
Password must only contain letter and digits 
Please enter a password: #### 
Password must have at least 8 characters 
Password must only contain letters and digits 
Please enter a password: abcd1234 
Password accepted! 

當我鍵入ABC，這是我所得到的：

Please enter password and then hit enter:abc 
Password must have at least 8 characters 
Password Accepted 

當我做這個節目結束！有人可以幫我解決這個問題嗎？先謝謝了。 =）另外，這是一個Java編程I類。

Answer 1

由於@cralfaro說你必須重複這個過程，如果密碼是無效的：

import java.util.Scanner; 
public class PasswordVerification { 

    public static void main(String[] args) { 
     //  Creates a scanner 
     Scanner sc = new Scanner(System.in); 
     boolean valid = false; 
     String password; 

     do { // start a loop 
      //  Asks user to enter password 
      System.out.print("Please enter password and then hit enter:"); 
      password = sc.nextLine(); 

      //  Checks to see if password is at least 8 characters. 
      if (password.length()<8) 
      { 
       valid = false; 
       System.out.println("Password must have at least 8 characters"); 
       continue; // skip to next iteration 
      } 

      //  Checks each character to see if it is acceptable. 
      for (int i = 0; i < password.length(); i++){ 
       char c = password.charAt(i); 

       if (  ('a' <= c && c <= 'z') // Checks if it is a lower case letter 
         || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter 
         || ('0' <= c && c <= '9') //Checks to see if it is a digit 
       ) 
       { 

        valid = true; 
       } 
       else 
       { 
        // tells the user that only letters & digits are allowed 
        System.out.println("Only letter & digits are acceptable."); 
        valid = false; 
        break; 
       } 

      } 
     } while(!valid); // verify if the password is valid, if not repeat the process 

     // if the password is valid, tell the user it's accepted 
     System.out.println("Password Accepted"); 
    } 


} 

這樣的程序會繼續要求用戶輸入，如果密碼是無效的。

編輯： 感謝GC_的評論，問題是我錯過了第一次檢查中的繼續聲明。

Answer 2

在打印密碼被接受之前，檢查密碼是否仍然有效。

if(valid==true) { 
    System.out.println("Password Accepted"); 
} 

編輯：你也可以添加這個。

else { 
    System.out.println("Password Denied"); 
} 

Answer 3

你的問題IST這部分代碼：

if ( ('a' <= c && c <= 'z') // Checks if it is a lower case letter 
    || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter 
    || ('0' <= c && c <= '9') //Checks to see if it is a digit 
    ) { valid = true; } 

在這裏，您重置valid到true，即使是與長度的第一檢查小於8已經失敗。 因此abc將失敗3.和打印Password must have at least 8 characters這是好的。然後它會通過4.，重置有效到true和打印Password Accepted。

所以，你要通過

if (!(// if the character is none of the options below, print error 
     ('a' <= c && c <= 'z') // Checks if it is a lower case letter 
    || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter 
    || ('0' <= c && c <= '9') //Checks to see if it is a digit 
    )) { 
     // tells the user that only letters & digits are allowed 
     System.out.println("Only letter & digits are acceptable."); 
     valid = false; 
     break; 
    } 

編輯的更換if (...) { valid = true; } else { ... }部分： 你也應該首先設置boolean valid = true;代替false，只要你想將其設置爲false，只有當它失敗的條件。 然後在你的代碼的末尾，添加一個條件檢查周圍的最後輸出線valid，像

if(valid) { 
    System.out.println("Password Accepted"); 
} 

Answer 4

有點混亂，但試試這個：

public static void main(String[] args) { 
//  Creates a scanner 
Scanner sc = new Scanner(System.in); 
boolean valid = false; 
String password; 


//  Asks user to enter password 
while(true){ 
System.out.print("Please enter password and then hit enter:"); 
password = sc.nextLine(); 

//  Checks to see if password is at least 8 characters. 
if (password.length()<8) 
    { 
     valid = false; 
     System.out.println("Password must have at least 8 characters"); 
    } 
else { 

//  Checks each character to see if it is acceptable. 
for (int i = 0; i < password.length(); i++){ 
      char c = password.charAt(i); 

      if (  ('a' <= c && c <= 'z') // Checks if it is a lower case letter 
        || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter 
        || ('0' <= c && c <= '9') //Checks to see if it is a digit 
      ) { 
       valid = true; 
      } else { 
       System.out.println("Password denied"); 
       System.out.println("Only letter & digits are acceptable."); 
       valid = false; 
       break; 
      } 


} 

if (valid == true) { 
System.out.println("Password accepted"); 
    break; 
     }    
} 
} 
}