令人困惑的数字格式异常答案

【问题标题】：Confusing number format exceptions令人困惑的数字格式异常
【发布时间】：2017-09-18 03:10:09
【问题描述】：

我收到一大堆似乎源于我的解析双精度的异常，因为它们的信息是：线程“AWT-EventQueue-0”中的异常java.lang.NumberFormatException：空字符串另一个可能的嫌疑人是

account1.withdrawl(checkingBal, changeValue) ;

尽管我在被调用的方法中使用了 try catch 块，但确信这是一个未报告的异常：

public double withdrawl(double currentBal, double withdrawlAmount) throws InsufficientFunds{
    int i =0 ;
    double overDraw = 0 ;
    try{
    //verifies that input was numeric and evenly divisible by 20
  if(withdrawlAmount % 20 == 0){
    if(i>4){
        if(currentBal>1.5){
        currentBal = currentBal-1.5 ;
        }else{
        JOptionPane.showMessageDialog(null, "Insufficient funds");
        overDraw = currentBal-1.5 ;
        throw new InsufficientFunds(overDraw); 
        }
    }
    //stops withdrawl for insufficient funds
    if(currentBal<withdrawlAmount) {
        JOptionPane.showMessageDialog(null, "Insufficient funds");
        overDraw = currentBal-withdrawlAmount ;
        throw new InsufficientFunds(overDraw);
    }else {
        currentBal=currentBal-withdrawlAmount ;
    }
    i++ ;
  }else {
  JOptionPane.showMessageDialog(null, "Please enter a withdarl amount that is divisible by 20");
  }
    }catch (InsufficientFunds ex){
        ex.getAmount();
    }
  return currentBal ;
 }




public class ATM extends JFrame implements ActionListener {
JButton withdraw, deposit, transfer, balance ;
JTextField input ;
boolean checkingActive = true ;
public double checkingBal = 0 ;
public double savingsBal = 0 ;

主类：

ATM(){
withdraw = new JButton ("Withdraw") ;
deposit = new JButton ("Deposit") ;
transfer = new JButton ("Transfer") ;
balance = new JButton ("Balance") ;
input = new JTextField (12) ;
input.setText("0") ;
input.setEditable(true) ;

JRadioButton checking = new JRadioButton("Checking", true) ;;
JRadioButton savings = new JRadioButton("Savings") ;
this.add(checking);
this.add(savings);
ButtonGroup acctSelector = new ButtonGroup();
acctSelector.add(checking);
acctSelector.add(savings);


add(withdraw);
add(deposit);
add(transfer);
add(balance);
add(input);

//assigns buttons to logic gorup
ButtonGroup accountChoice = new ButtonGroup();
accountChoice.add(checking) ;
accountChoice.add(savings) ;

input = new JTextField(6) ;

//assigns listeners to buttons
withdraw.addActionListener(this) ;
deposit.addActionListener(this) ;
transfer.addActionListener(this) ;
balance.addActionListener(this) ;

setSize(500,400) ;
setLayout(new FlowLayout()) ;
setTitle("MoneyBank ATM") ;
}

//acceses account changes
public void actionPerformed(ActionEvent e){
 double changeValue = Double.parseDouble(input.getText().trim());
 Account account1 = new Account() ;
 if(checkingActive==true){
    if(e.getSource()== withdraw){
      account1.withdrawl(checkingBal, changeValue) ;
    } else if(e.getSource()== deposit) {
       account1.deposit(checkingBal, changeValue) ;
    } else if(e.getSource()== transfer){
       account1.transfer(checkingBal, changeValue) ;
    } else {
       account1.balance(checkingBal) ;
    }
 } else {
    if(e.getSource()== withdraw){
      account1.withdrawl(savingsBal, changeValue) ;
    } else if(e.getSource()== deposit) {
       account1.deposit(savingsBal, changeValue) ;
    } else if(e.getSource()== transfer){
       account1.transfer(savingsBal, changeValue) ;
    } else {
       account1.balance(savingsBal) ;  
    }
 }
JOptionPane.showMessageDialog(null, "Current balances are: \n Savings: " + savingsBal + "\n Checking: "+ checkingBal);
}

//constructs atm object/GUI
public static void main(String[] args){
ATM account=new ATM();
account.setVisible(true);
account.setLocation(200,200);
account.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

public boolean pickAccount(boolean k) {
   checkingActive = k ;
   return checkingActive ;
}

}

【问题讨论】：

当我在 withdawl 代码中加上 try - catchs 时，它并没有改变任何东西，所以我最好的猜测仍然是解析。但我有一个默认值，所以我不确定它为什么会出现问题
环顾四周时意识到我从来没有为我的单选按钮设置正确的操作命令，所以我会看看修复它是否有任何作用。编辑：它没有，但至少我解决了我的问题的那一部分
最好在执行此操作之前进行数据验证 Double.parseDouble(input.getText().trim())
一个公平的观点，但我正在输入似乎可以接受的值，它仍然会触发异常
尝试在调用withdrawl()之前打印出输入的值，异常似乎不是来自withdrawl内部。异常本身是否会显示哪行代码抛出了错误？

标签： java exception number-formatting

【解决方案1】：

您正在为变量输入创建 2 个不同的 JTextField 实例。

第一个：

input = new JTextField(12);
input.setText("0");
input.setEditable(true);

第二个：

input = new JTextField(6);

因此，当您在字段中写入一个数字并将该值发送到处理时，您收到的是一个空值“”。最后，您的应用程序尝试从该空导致生成 Double：

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String

您可以评论或删除第二个实例，您的应用程序将正常运行。

【讨论】：