序列化對象被覆蓋，不添加到

Question

我試圖存儲用戶賬戶信息到一個單獨的文本文件，我已經多次嘗試後完成...

但是每一次我創建覆蓋的新用戶最後一個放入文件中。 另外，存儲的唯一東西是字符串，我有一個PIN號碼和一個賬戶餘額，我以後需要的是非常重要的。

這是我到目前爲止，我認爲問題是每次我運行代碼Object命名用戶正在創建，並且因爲它不是動態的，它只是每次都覆蓋自己。

在序列化任何東西時我都是noob，所以如果你能用最簡單的話來解釋這個問題，那就太棒了！

的目標是讓我能夠存儲每一個新的用戶帳戶，然後回來在稍後將它們顯示給用戶，如果帳戶信息的引腳數量和用戶名

public class ATM implements Serializable { 

public static void main(String[] args) { 

    // variables 
    String dash = "-------------------\n"; 
    int accounts = 0; 

    // Scanner 
    Scanner scanner = new Scanner(System.in); 

    // Welcome screen 
    System.out.print(dash); 
    System.out.print("Welcome to the Bank\n"); 
    System.out.print(dash); 

    System.out.println("Do you have an account with us? (y/n) "); 

    String answer = scanner.nextLine(); 

    if (answer.equalsIgnoreCase("y")) { 

    } else { 

     // new user is created 
     Bank bank = new Bank(); 

     accounts++; 

     System.out 
       .println("Enter your full name below (e.g. John M. Smith): "); 
     String name = scanner.nextLine(); 
     System.out.println("Create a username: "); 
     String userName = scanner.nextLine(); 
     System.out.println("Enter your starting deposit amount: "); 
     int balance = scanner.nextInt(); 

     System.out.print(dash); 
     System.out.print("Generating your information...\n"); 
     System.out.print(dash); 

     int pin = bank.PIN(); 
     String accountNum = bank.accountNum(); 

     String id = name + accountNum; 

     User user = new User(name, userName, pin, accountNum, balance); 

     // new user gets added to the array list 
     Bank.users.add(user); 

     String test = "Test989898998"; 

     System.out.println(user); 

     try { 
      FileOutputStream fileOut = new FileOutputStream("users.txt"); 

      ObjectOutputStream out = new ObjectOutputStream(fileOut); 

      out.writeObject(Bank.users); 
      out.close(); 
      fileOut.close(); 

     } catch (IOException i) { 
      i.printStackTrace(); 
     } 
    } 

} 

} 

匹配銀行類

public class Bank implements Serializable { 

//Generate a random 16 digit bank account number 
public String accountNum() { 

    int max = 9999; 
    int min = 1000; 

    int a1 = (int) (Math.random() * (max - min) + min); 
    int a2 = (int) (Math.random() * (max - min) + min); 
    int a3 = (int) (Math.random() * (max - min) + min); 
    int a4 = (int) (Math.random() * (max - min) + min); 

    String accountNum = a1 + "-" + a2 + "-" + a3 + "-" + a4; 

    return accountNum; 
} 

//Generate a random 4 digit PIN 
public int PIN() { 

    int max = 9999; 
    int min = 1000; 

    int PIN = (int) (Math.random() * (max - min) + min); 

    return PIN; 
} 

//array list for users 
static ArrayList<User> users = new ArrayList<User>() { 

}; 

} 

用戶類別

public class User implements Serializable{ 

String name; 
String userName; 
String accountNum; 
int pin; 
int balance; 

public User (String name, String userName, int pin, String accountNum, int balance) { 

    this.name = name; 
    this.userName = userName; 
    this.accountNum = accountNum; 
    this.pin = pin; 
    this.balance = balance; 
} 

public String toString() { 

    return "Name: " + this.name + "\n\nUsername: " + this.userName + " | " + "Pin: " + this.pin + "\n\n" 
      + "Account Number: " + this.accountNum + "\n\nAccount Balance: $" + this.balance + 
      "\n\nNever share your login information with anyone!"; 
} 

} 

Answer 1

但是，每次我創建一個新用戶時，它都會覆蓋放入文件的最後一個用戶。

這是正確的。你不是追加到文件中，而是創建一個新文件。這與對象或序列化無關，它只是您正在使用的FileOutputStream的構造函數的問題。

但是，沒有使用我不會在這裏引用的技巧，你不能追加到對象流，因爲有一個頭會混淆後續的讀者。您需要閱讀整個文件並再次寫出。最簡單的方法是序列化一個ArrayList<User>而不是User對象本身。