Question

我的计算机科学课的任务是抛出异常。该作业创建了一个小程序来管理用户的银行帐户。

我的问题如下：只有当用户试图提取的金额超过余额时才需要抛出异常（InsufficientFundsException）。但是，我只想在提款而不是存款的情况下抛出InsufficientFundsException。

以下是问题主要针对我遇到问题的部分的方法的代码：

actionPerformed方法（我正在实现ActionListener接口）

此方法需要根据点击的按钮 - 存款或取款按钮 - 处理该交易方法。事务方法只是将传递给方法的金额加到或减去Account对象的余额。然后，如果有异常，它将捕获异常并打印错误等。但是当前捕获的异常同时适用于撤销和存款交易，而仍然需要抛出的那个 - InsufficientFundsException - 仅适用于撤回交易。另外，我无法修改Account对象中的withdraw方法以抛出异常。

getAmount方法：

我没有选择在此方法中抛出InsufficientFundsException

我试着添加这个：

if(getAmount(tf4) > acc1.getBalance())
{
  throw InsufficientFundsException("Insufficient Funds");
}

在退出电话会议之前

：

 if (e.getSource() == withdraw)
 {
   try
   {
     acc1.withdraw(getAmount(tf4));
     refreshFields();
     status.setText("Withdrawal Processed");
   }
   catch(EmptyFieldException ex)
   {
     status.setText(ex.getMessage() + "withdraw");
   }
   catch(NumberFormatException ex)
   {
     status.setText(ex.getMessage() + "withdraw");
   }
   catch(NegativeAmountException ex)
   {
     status.setText(ex.getMessage() + "withdraw");
   }
 }

但是我收到错误，因为actionPerformed方法不能throws InsufficientFundsException。

另外如果我在一个try / catch块中尝试catch一个InsufficientFundsException，我得到另一个try / catch块的错误，因为我没有捕获异常...因为我不想要抓住那个例外。

根据要求，这是完整的代码：

import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
import java.text.*;

public class AccountApplet extends JApplet implements ActionListener
{  
  Container c = getContentPane();
  JPanel p1 = new JPanel(),
         p2 = new JPanel(),
         p3 = new JPanel(),
         p4 = new JPanel();
  JLabel lab1 = new JLabel("Account ID");
  JLabel lab2 = new JLabel("Account Balance");
  JLabel lab3 = new JLabel("Deposit");
  JLabel lab4 = new JLabel("Withdraw");
  JLabel status = new JLabel("Status Bar");
  JTextField tf1 = new JTextField(),
             tf2 = new JTextField(),
             tf3 = new JTextField(),
             tf4 = new JTextField();
  JButton deposit = new JButton("Deposit"),
          withdraw = new JButton("Withdraw");
  Account acc1 = new Account(1234, 1000.00);
  double amount;

  public void init()
  {           
    tf1.setEditable(false);
    tf2.setEditable(false);       
    c.setLayout(new BorderLayout());
    c.add(p1, BorderLayout.WEST);
    p1.setBorder(new TitledBorder("Display Account Information"));
    p1.setLayout(new GridLayout(2,2));
    p1.add(lab1);
    p1.add(tf1);
    p1.add(lab2);
    p1.add(tf2);
    c.add(p2, BorderLayout.EAST);
    p2.setBorder(new TitledBorder("Deposit or Withdraw Funds"));
    p2.setLayout(new BorderLayout());
    p2.add(p3, BorderLayout.WEST);
    p2.add(p4, BorderLayout.EAST);
    p3.setLayout(new GridLayout(2,1));
    p3.add(lab3);
    p3.add(lab4);
    p4.setLayout(new GridLayout(2,2));
    p4.add(tf3);
    p4.add(deposit);
    p4.add(tf4);
    p4.add(withdraw);
    c.add(status, BorderLayout.SOUTH);
    deposit.addActionListener(this);
    withdraw.addActionListener(this);
    refreshFields();     
  }

  public void actionPerformed(ActionEvent e)
  {
    status.setText("");
    if (e.getSource() == deposit)
    {
      try
      {
        acc1.deposit(getAmount(tf3));
        refreshFields();
        status.setText("Withdrawal Processed");
      }
      catch(EmptyFieldException ex)
      {
        status.setText(ex.getMessage() + "deposit");
      }
      catch(NumberFormatException ex)
      {
        status.setText(ex.getMessage() + "deposit");
      }
      catch(NegativeAmountException ex)
      {
        status.setText(ex.getMessage() + "deposit");
      } 
    }
    if (e.getSource() == withdraw)
    {
      try
      {
        acc1.withdraw(getAmount(tf4));
        refreshFields();
        status.setText("Withdrawal Processed");
      }
      catch(EmptyFieldException ex)
      {
        status.setText(ex.getMessage() + "withdraw");
      }
      catch(NumberFormatException ex)
      {
        status.setText(ex.getMessage() + "withdraw");
      }
      catch(NegativeAmountException ex)
      {
        status.setText(ex.getMessage() + "withdraw");
      }
    }
  }

  public void refreshFields()
  {
    tf1.setText(String.valueOf(acc1.getId()));
    tf2.setText("$" + String.valueOf(acc1.getBalance()));
    tf3.setText("");
    tf4.setText("");
    status.setText("");
  }

  public double getAmount(JTextField tf)  throws EmptyFieldException ,
                                                NumberFormatException,
                                                NegativeAmountException
  { 

    if(tf.getText().equals(""))
    {
      throw new EmptyFieldException("Empty field not allowed for ");
    }
    try
    {
      amount = Double.parseDouble(tf.getText());
    }
    catch(Throwable ex)
    {
      throw new NumberFormatException("Insufficient funds", ex);
    }
    if(amount < 0)
    {
      throw new NegativeAmountException("Negative amount not allowed for ");
    }

    else
    { 
      return Double.parseDouble(tf.getText());
    }
  }

}

帐户类代码：

public class Account
{
  private int id;
  private double balance;

  Account(int id, double balance)
  {
    this.id = id;
    this.balance = balance;
  }

  public int getId()
  {
    return id;
  }

  public double getBalance()
  {
    return balance;
  }

  public void setBalance(double balance)
  {
    this.balance = balance;
  }

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

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

异常代码：

public class EmptyFieldException extends Exception
{
  EmptyFieldException(String message)
  {
    super(message);
  }
}

，

public class InsufficientFundsException extends Exception
{
  InsufficientFundsException(String message)
  {
    super(message);
  }
}

，

public class NegativeAmountException extends Exception
{
  NegativeAmountException(String message)
  {
    super(message);
  }
}

任何人都可以帮助我吗？我应该在哪里抛出这个例外？

Answer 1

使用异常链接机制。例如尝试这样的事情。

if (e.getSource() == withdraw) {
   try
   {
     if(getAmount(tf4) > acc1.getBalance())
     {
         throw InsufficientFundsException("Insufficient Funds");
     }
     acc1.withdraw(getAmount(tf4));
     refreshFields();
     status.setText("Withdrawal Processed");
   }
   catch(InsufficientFundsException ex)
   {
      //rethrow some unchecked exception like IllegalArgumentException
      //or your own checked exception like EmptyFieldException 
      throw new EmptyFieldException("some message", ex);

      //or add the exception message and trace to status.
      status.setText(ex.getMessage() + "withdraw");
   }
   catch(EmptyFieldException ex)
   {
      status.setText(ex.getMessage() + "withdraw");
   }
   catch(NumberFormatException ex)
   {
      status.setText(ex.getMessage() + "withdraw");
   }
   catch(NegativeAmountException ex)
   {
     status.setText(ex.getMessage() + "withdraw");
   }
}

在您的代码中确定没有办法有意义地抛出InsufficientFundsException。最好的方法是避免它，只需使用status.setText（）直接在if检查中打印消息。

     if(getAmount(tf4) > acc1.getBalance())
     {
         status.setText("Insufficient Funds - Withdraw cancelled");
     }

仅在一种情况下抛出异常

1 个答案: