在 AccountApplet 中我试图显示错误消息“Empty field not allowed for deposit”，其中一部分是通过 getMessage 方法完成的，另一半是不允许存款的，
但是在我的程序中，getMessage 方法产生“空字符串”，而不是“空字段”，我将如何进行更改？
getMessage 方面在 actionPerformed 方法中完成
这是 AccountApplet 类
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.border.*;
import java.text.NumberFormat;
public class AccountApplet extends JApplet implements ActionListener
{
// For West
public JLabel ai = new JLabel("Account ID ");
public JTextField aitf = new JTextField();
public JLabel ab = new JLabel("Account Balance ");
public JTextField abtf = new JTextField();
// For East
public JButton dp = new JButton ("Deposit");
public JTextField dptf = new JTextField();
public JButton wt = new JButton ("Withdraw");
public JTextField wttf = new JTextField();
// For South
public JLabel status = new JLabel("");
Account account = new Account(1234,1000); // ******** here *******
public void init()
{
this.setSize(400, 90);
//----------------------
// Set up the Structure
//----------------------
Container c = getContentPane();
JPanel b = new JPanel(new BorderLayout());
JPanel west = new JPanel(new GridLayout(2,2));
JPanel east = new JPanel(new BorderLayout());
JPanel depo_with = new JPanel(new GridLayout(2,2));
// Add BorderLayout to the container
c.add(b);
// Add everything to West
b.add(west, BorderLayout.WEST);
west.setBorder(new TitledBorder("Display Account Information"));
west.add(ai);
west.add(aitf);
aitf.setEditable(false);
west.add(ab);
west.add(abtf);
abtf.setEditable(false);
// Add everything to EAST
b.add(east, BorderLayout.EAST);
east.setBorder(new TitledBorder("Deposit or Withdrawl Funds"));
east.add(depo_with, BorderLayout.EAST);
depo_with.add(dptf);
depo_with.add(dp);
depo_with.add(wttf);
depo_with.add(wt);
dp.addActionListener(this);
wt.addActionListener(this);
// Add everything to SOUTH
b.add(status, BorderLayout.SOUTH);
refreshFields();
} // End intit
//-------------------------------------------------------------------------------------------------------------------------------------------------------
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == dp) // Executes if deposit was clicked
{
try
{
getAmount(dptf);
account.deposit(Double.parseDouble(dptf.getText()));
account.setBalance(account.balance);
status.setText("Deposit processed");
refreshFields();
}
catch (NegativeAmountException nae)
{
status.setText(nae.getMessage() + " not allowed for deposit");
}
catch (EmptyFieldException efe)
{
status.setText(efe.getMessage() + " not allowed for deposit");
}
catch (Exception ex)
{
status.setText(ex.getMessage() + " not allowed for deposit");
}
}
if (e.getSource() == wt) // Executes if withdraw was clicked
{
try
{
getAmount(wttf);
account.withdraw(Double.parseDouble(wttf.getText()));
account.setBalance(account.balance);
status.setText("Withdraw processed");
refreshFields();
}
catch (InsufficientFundsException ife)
{
status.setText(ife.getMessage() + " Insufficient funds");
}
catch (NegativeAmountException nae)
{
status.setText(nae.getMessage() + " not allowed for withdraw");
}
catch (EmptyFieldException efe)
{
status.setText(efe.getMessage() + " not allowed for withdraw");
}
catch (Exception ex)
{
status.setText(ex.getMessage() + " not allowed for withdraw");
}
}
} // end ActionPerformed
public void refreshFields()
{
NumberFormat fmt = NumberFormat.getCurrencyInstance();
aitf.setText("" + account.getId() );
abtf.setText("" + fmt.format(account.getBalance()));
// diplays accound id and balance in left text fields
//should be called when the applet is first displayed and after each valid transaction
}
public double getAmount(JTextField tf) throws EmptyFieldException,
NumberFormatException,
NegativeAmountException
{
double depo;
try
{
depo = Double.parseDouble(dptf.getText()); // read in one textfield and convert to a number
}
catch (NumberFormatException nfe) // catch NumberFormatException
{
throw nfe; // catch throws NumberFormatException
}
return depo;
} // End
} // End Class
账户类
import java.awt.*;
import java.awt.event.*;
public class Account
{
int id = 1234;
double balance = 1000.00;
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) throws NegativeAmountException
{
if ( balance < 0)
throw new NegativeAmountException();
this.balance = balance;
}
public void deposit(double amount) throws NegativeAmountException
{
if (amount < 0)
throw new NegativeAmountException();
balance += amount;
}
public void withdraw(double amount) throws NegativeAmountException,
InsufficientFundsException
{
if (amount > balance )
{
throw new NegativeAmountException();
}
if (amount > balance )
{
throw new InsufficientFundsException();
}
balance -= amount;
}
}
空域异常
public class EmptyFieldException extends Exception
{
EmptyFieldException()
{
super();
}
}
资金不足异常
public class InsufficientFundsException extends Exception
{
InsufficientFundsException()
{
super();
}
}
负金额异常
public class NegativeAmountException extends Exception
{
NegativeAmountException()
{
super();
}
}