JTextField 只显示绝对值，没有负号？

Question

我正在开发一个“银行账户”类型的程序，我的目标是取款和存款，显示更新后的余额，显示账户状态（是否透支）。我刚刚得到了加/减和更新平衡工作，但是我的 JTextFields 中的数字是绝对值，并且不显示负余额（余额

     depositButton.addActionListener(new DepositListener());
     withdrawButton.addActionListener(new WithdrawListener());

    //create object of BankAccount, assign values to the text fields
     BankAccount myAcct = new BankAccount(1524687, 100.00, "Landon Wiggs");
     acctNameF.setText(myAcct.getName() );
     acctNumF.setText(Integer.toString( myAcct.getAcctNumber() ) );
     acctBalanceF.setText( Double.toString(myAcct.getBalance()));
     depositWithdrawAmtF.setText("0.00");


  private class DepositListener implements ActionListener 
{
      public void actionPerformed (ActionEvent event)
      {  
         double sum = Double.valueOf(depositWithdrawAmtF.getText()) + Double.valueOf(acctBalanceF.getText());
         double amt = (Double.parseDouble(depositWithdrawAmtF.getText()));
         acctBalanceF.setText(Double.toString(sum)); 
      }
   }

private class WithdrawListener implements ActionListener {
      public void actionPerformed (ActionEvent event) {
         double sum = (Double.valueOf(depositWithdrawAmtF.getText() )) - (Double.valueOf(acctBalanceF.getText() ));
         double amt = (Double.parseDouble(depositWithdrawAmtF.getText()));

         acctBalanceF.setText(Double.toString(sum));   
      }
   }

Answer 1

当您提款时，您可能应该从账户资金中减去提款金额，现在您正在做相反的事情。

改变

double sum = (Double.valueOf(depositWithdrawAmtF.getText() )) - (Double.valueOf(acctBalanceF.getText() ));

到

double sum = Double.valueOf(acctBalanceF.getText()) - Double.valueOf(depositWithdrawAmtF.getText());