使用Aspectj的银行帐户程序

Question

我想编写一个跟踪银行帐户的Java程序

现在我有以下简单程序：

public class account
{
    private double balance;
    private String owner;
    public account(double x, String s) { balance=x; owner=s; }
    public String owner() { return owner; }
    public void withdraw(double a) { balance -= a; }
    public void deposit(double a) { balance += a; }
    public void printbalance() { System.out.println(balance); }

    // main for testing:
public static void main(String[] argv)
{
      account a1 = new account(2000,"you boss");
      account a2 = new account(1000,"me nerd");
      a1.deposit(400);
      a2.withdraw(300000);   // not enough money!
      a2.withdraw(-500000); // trying to cheat!
      a1.printbalance();
      a2.printbalance();
}//main
} // account

并且我想使用aspectj将以下内容添加到该程序中：

1-我想防止帐户提取更多的当前余额并提取负数。

2-我也希望它防止存入负数。

3-我需要添加图形界面，（按钮）

4-添加需要在客户进行交易之前输入的密码或密码。

5-跟踪帐户上的所有交易（取款和存款，并在需要时打印报告。

非常感谢您的帮助。谢谢。

privileged aspect newAccount
{
  //withdraw (prevent withdraw negative numbers and number greater than the   //current balance) 
    void around(account a, double x) : execution(void account.withdraw(double)) && target(a) && args(x){
        if(x > a.balance){
            System.out.println("not enough money!");
            return;
        }else if(x < 0){
            System.out.println("trying to cheat!");
            return;
        }
        proceed(a, x);
    }

//Deposit: prevent deposit negative number
    void around(double x) : execution(void account.deposit(double)) && args(x){
        if(x < 0){
            System.out.println("trying to  deposit negtive money!");
            return;
        }
        proceed(x);
    } 

    after() : execution(public static void *.main(String[])){
        account.a3 = new account(3000,"he nerd");
        a3.deposit(-100);
        a3.printbalance();

    }

//To Do: pin secret password 
//To Do: Transaction Record
}

Answer 1

我可以看到您仍在学习Java，因为您不了解诸如此类的基本编程约定

• 类名应以大写字母开头，
• 变量，参数和字段应具有易于理解的名称，而不是单个字母。

您还从特权方面使用直接字段访问，而不仅仅是为类的字段创建公共getter方法并使用它们。 toString方法也很有用，因为这样您就可以轻松地打印对象，而无需访问getter和构造自己的输出。

此外，在main方法之后运行的建议是一个不错的实验，但没有太大意义。由于帐户所有者与您的应用程序中的帐户所有者之一具有相同的名称，因此您似乎想要入侵该帐户。我在这里注释了代码，以解释为什么它不能那样工作。

我还重构了您的应用程序类和方面，现在看起来像这样，而没有更改功能：

package de.scrum_master.app;

public class Account {
  private String owner;
  private double balance;

  public Account(String owner, double balance) {
    this.owner = owner;
    this.balance = balance;
  }

  public void withdraw(double amount) {
    balance -= amount;
  }

  public void deposit(double amount) {
    balance += amount;
  }

  public String getOwner() {
    return owner;
  }

  public double getBalance() {
    return balance;
  }

  @Override
  public String toString() {
    return "Account[owner=" + owner + ", balance=" + balance + "]";
  }

  public static void main(String[] argv) {
    Account bossAccount = new Account("Boss", 2000);
    Account nerdAccount = new Account("Nerd", 1000);
    bossAccount.deposit(400);
    nerdAccount.withdraw(200);
    bossAccount.withdraw(300000);    // Cannot withdraw more than account balance
    nerdAccount.withdraw(-500000);   // Cannot withdraw a negative amount
    bossAccount.deposit(-123456);    // Cannot deposit a negative amount
    System.out.println(bossAccount);
    System.out.println(nerdAccount);
  }
}

package de.scrum_master.aspect;

import de.scrum_master.app.Account;

public aspect AccountAspect {

  // Withdrawal
  void around(Account account, double amount) :
    execution(void Account.withdraw(double)) &&
    target(account) &&
    args(amount)
  {
    if (amount > account.getBalance()) {
      System.out.println("Cannot withdraw more than account balance");
      return;
    }
    if (amount < 0) {
      System.out.println("Cannot withdraw a negative amount");
      return;
    }
    proceed(account, amount);
  }

  // Deposit
  void around(double amount) :
    execution(void Account.deposit(double)) &&
    args(amount)
  {
    if (amount < 0) {
      System.out.println("Cannot deposit a negative amount");
      return;
    }
    proceed(amount);
  }

  // This does not make any sense because
  //   1. it happens after the application ends (after leaving main method)
  //   2. Even though the account owner is the same as in the main method,
  //      it does not mean that by creating a new object with the same name
  //      the "Nerd" can manipulate the original account balance. You have to
  //      intercept the original Account object and manipulate it directly.
  after() : execution(public static void *.main(String[])) {
    System.out.println("--- after end of main program ---");
    Account account = new Account("Nerd", 3000);
    account.deposit(-100);
    System.out.println(account);
  }

  // TODO: PIN secret password
  // TODO: transaction record
}

控制台日志将是：

Cannot withdraw more than account balance
Cannot withdraw a negative amount
Cannot deposit a negative amount
Account[owner=Boss, balance=2400.0]
Account[owner=Nerd, balance=800.0]
--- after end of main program ---
Cannot deposit a negative amount
Account[owner=Nerd, balance=3000.0]

我不会为您做家庭作业，但会给您一些提示：

• PIN（秘密密码）：Account类需要可以在构造函数中设置的字段pin，并且不应具有公共getter方法，以避免任何人都可以访问PIN。如果分配要求您不编辑基类而是通过AOP解决问题，则可以使用类型间定义（ITD）来添加私有字段和公共设置器，甚至可以向该类添加其他构造函数。接下来，您将添加一条建议，要求用户首次尝试访问某个帐户的任何交易方法（例如deposit和withdraw）时，请在控制台上输入PIN。正确输入PIN后，他将能够继续操作，否则将出现错误消息，并且交易将被禁止。方面本身可以保留所有Account对象（可能要使用Set<Account>）的缓存（临时存储），该对象在运行会话期间已成功通过身份验证，从而避免了用户必须输入PIN再次使用同一帐户。

• 每个帐户的交易记录：同样，您可以使用ITD将List<TransactionRecord>之类的字段添加到Account，使用空列表初始化它，然后为每个存款或退出。您也可以简化概念证明，而不是创建TransactionRecord助手类，而仅使用List<Double>进行交易，记录正存款金额和负存款金额。带有“存款123.45”或“提款67.89”之类的List<String>也是可行的选择。重要的是您的老师可以看到正确的方面逻辑。