使用GUI的Java空指针异常错误

所以，我正在编写一个模仿使用GUI的支票帐户的程序。我的某个功能有问题。我创建一个Transaction对象并调用一个检查帐户的函数，将Transaction帐户添加到Checkingaccount类中的Transaction arraylist中。但是，每次调用该函数时，都会收到空指针异常错误。我怎样才能解决这个问题？使用GUI的Java空指针异常错误

代码：

public class CheckingAccount 
{ 
    private double balance; 
    private double totalServiceCharge; 
    private ArrayList<Transaction> transList; 
    private int transCount; 

public CheckingAccount(double initialVal) 
    { 
     balance = initialVal; 
     totalServiceCharge = 0; 
     transCount = 0; 
    } 

    public double getBalance() 
    { 
     return balance; 
    } 

    public void setBalance(double transAmt, int tCode) 
    { 
     if(tCode == 1) 
     { 
      balance -= transAmt; 

     } 
     else if(tCode == 2) 
     { 
      balance += transAmt; 
     } 
    } 

    public double getServiceCharge() 
    { 
     return totalServiceCharge; 
    } 

    public void setServiceCharge(double currentServiceCharge) 
    { 
     totalServiceCharge += currentServiceCharge; 
    } 

    public void addTrans(Transaction newTrans) 
    { 
     transList.add(newTrans); 
     transCount++; 
    } 

    public int getTransCount() 
    { 
     return transCount; 
    } 

    public Transaction getTrans(int i) 
    { 
     return transList.get(i); 
    } 

} 

public class Transaction 
{ 
    private int transNumber; 
    private int transId; 
    private double transAmt; 

    public Transaction(int num, int id, double amt) 
    { 
     transNumber = num; 
     transId = id; 
     transAmt = amt; 
    } 

    public int getTransNumber() 
    { 
     return transNumber; 
    } 

    public int getTransId() 
    { 
     return transId; 
    } 

    public double getTransAmount() 
    { 
     return transAmt; 
    } 
} 

public class OptPanel extends JPanel 
{ 
    private JLabel label; 
    private JRadioButton button1, button2, button3, button4; 

    public OptPanel() 
    {  
     label = new JLabel("Choose Action:"); 
     label.setFont(new Font("Helvetica", Font.BOLD, 24)); 

     button1 = new JRadioButton("enter transaction"); 
     button2 = new JRadioButton("list all transactions"); 
     button3 = new JRadioButton("list all checks"); 
     button4 = new JRadioButton("list all deposits"); 

     ButtonGroup group = new ButtonGroup(); 
     group.add(button1); 
     group.add(button2); 
     group.add(button3); 
     group.add(button4); 

     OptListener listener = new OptListener(); 

     button1.addActionListener(listener); 
     button2.addActionListener(listener); 
     button3.addActionListener(listener); 
     button4.addActionListener(listener); 

     add(label); 
     add(button1); 
     add(button2); 
     add(button3); 
     add(button4); 

     setBackground(Color.yellow); 
     setPreferredSize(new Dimension(300,150)); 
    } 

    private class OptListener implements ActionListener 
    { 
     public void actionPerformed(ActionEvent event) 
     { 
      Object source = event.getSource(); 

      if(source == button1) 
      { 
       Main.doFunction(); 
      } 
      else if(source == button2) 
      { 
       Main.listTrans(); 
      } 
      else if(source == button3) 
      { 

      } 
      else if(source == button4) 
      { 

      } 
     } 
    } 
} 

public class Main 
{ 
    static String msg = JOptionPane.showInputDialog("Enter your initial balance:"); 
    static double amt = Double.parseDouble(msg); 

    static CheckingAccount checkAcc = new CheckingAccount(amt); 
    static Transaction trans = new Transaction(0, 0, 0); 

    public static void main(String[] args) 
    {  
     JFrame frame = new JFrame("Checking Account Actions"); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

     OptPanel panel = new OptPanel(); 
     frame.getContentPane().add(panel); 

     frame.pack(); 
     frame.setVisible(true); 
    } 

    public static int getTransCode() 
    { 
     String msg = JOptionPane.showInputDialog("Enter trans code: "); 
     return Integer.parseInt(msg); 
    } 

    public static double getTransAmt() 
    { 
     String msg = JOptionPane.showInputDialog("Enter trans amt: "); 
     return Double.parseDouble(msg); 
    } 

    public static void processCheck(CheckingAccount acc, double amt, int tcode) 
    { 
     acc.setBalance(amt, tcode); 
     if(acc.getBalance() < 0) 
     { 
      acc.setServiceCharge(10.15); 
     } 
     else 
     { 
      acc.setServiceCharge(0.15); 
     } 
    } 

    public static void processDeposit(CheckingAccount acc, double amt, int tcode) 
    { 
     acc.setBalance(amt, tcode); 
     acc.setServiceCharge(0.10); 
    } 

    public static void doFunction() 
    { 
     String msg; 
     int code; 
     double amt; 

     DecimalFormat fmt = new DecimalFormat ("$#,###,###.00;($#,###,###.00)"); 

     do 
     { 
      code = getTransCode(); 

      if(code == 1) 
      { 
       amt = getTransAmt(); 
       processCheck(checkAcc, amt, code); 

       if(checkAcc.getTransCount() == 0) 
       { 
        checkAcc.setServiceCharge(5); 
        msg = "Transaction: Check in amount of " + fmt.format(amt) + "\n Current Balance: " + 
          fmt.format(checkAcc.getBalance()) + "\n" + 
          "Service Charge: Check -- charge $0.15" + 
          (checkAcc.getBalance() < 50 ? "\nWarning: Balance below $50" : "") + 
          (checkAcc.getBalance() < 0 ? "\nService Charge: Below $0 -- charge $10.00" : "") + 
          "\nService Charge: Below $500 -- charge $5.00\nTotal Service Charge: " + 
          fmt.format(checkAcc.getServiceCharge()); 
        JOptionPane.showMessageDialog (null, msg); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 1, amt)); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 3, 0.15)); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 3, 5.00)); 
       } 
       else 
       { 
        msg = "Transaction: Check in amount of " + fmt.format(amt) + "\n Current Balance: " + 
          fmt.format(checkAcc.getBalance()) + "\n" + 
          "Service Charge: Check -- charge $0.15" + 
          (checkAcc.getBalance() < 50 ? "\nWarning: Balance below $50" : "") + 
          (checkAcc.getBalance() < 0 ? "\nService Charge: Below $0 -- charge $10.00" : "") + 
          "\nTotal Service Charge: " + fmt.format(checkAcc.getServiceCharge()); 
        JOptionPane.showMessageDialog (null, msg); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 1, amt)); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 3, 0.15)); 
       } 

      } 
      else if(code == 2) 
      { 
       amt = getTransAmt(); 
       processDeposit(checkAcc, amt, code); 

       if(checkAcc.getTransCount() == 0) 
       { 
        System.out.println(checkAcc.getTransCount()); 
        checkAcc.setServiceCharge(5); 
        msg = "Transaction: Deposit in amount of " + fmt.format(amt) + "\n Current Balance: " + 
          fmt.format(checkAcc.getBalance()) + "\n" + 
          "Service Charge: Deposit -- charge $0.10" + 
          (checkAcc.getBalance() < 50 ? "\nWarning: Balance below $50" : "") + 
          (checkAcc.getBalance() < 0 ? "\nService Charge: Below $0 -- charge $10.00" : "") + 
          "\nService Charge: Below $500 -- charge $5.00\nTotal Service Charge: " + 
          fmt.format(checkAcc.getServiceCharge()); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 2, amt)); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 3, 0.10)); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 3, 5.00)); 
        JOptionPane.showMessageDialog (null, msg); 
       } 
       else 
       { 
        msg = "Transaction: Deposit in amount of " + fmt.format(amt) + "\n Current Balance: " + 
          fmt.format(checkAcc.getBalance()) + "\n" + 
          "Service Charge: Deposit -- charge $0.10" + 
          (checkAcc.getBalance() < 50 ? "\nWarning: Balance below $50" : "") + 
          (checkAcc.getBalance() < 0 ? "\nService Charge: Below $0 -- charge $10.00" : "") + 
          "\nTotal Service Charge: " + fmt.format(checkAcc.getServiceCharge()); 
        JOptionPane.showMessageDialog (null, msg); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 2, amt)); 
        checkAcc.addTrans(new Transaction(checkAcc.getTransCount(), 3, 0.10)); 
       } 
      } 

     }while(code != 0); 

     msg = "Transaction: End\n Current Balance: " + fmt.format(checkAcc.getBalance()) + 
       "\nTotal Service Charge: " + fmt.format(checkAcc.getServiceCharge()) + "\n" + 
       "Final Balance: " + fmt.format(checkAcc.getBalance() - checkAcc.getServiceCharge()); 
     JOptionPane.showMessageDialog (null, msg); 
    } 

    public static void listTrans() 
    { 
     JTextArea text = new JTextArea(); 
     String message = ""; 
     int num; 
     text.setOpaque(false); 
     text.setFont(new Font("Monospaced", Font.PLAIN, 14)); 
     text.setBorder(null); 
     message+="ID  Type  Amount\n\n"; 
     for(num=0; num < checkAcc.getTransCount(); num++) 
     { 
      message += String.format("%3d   %-9s    %6d\n", num, 
        (checkAcc.getTrans(num).getTransId() == 1 ? "Check" : 
         (checkAcc.getTrans(num).getTransId() == 2 ? "Deposit" : "Svc. Charge")), 
        checkAcc.getTrans(num).getTransAmount()); 
     } 
     text.setText(message); 
     JOptionPane.showMessageDialog(null, text); 
    } 
}

在此先感谢。

来源

2015-04-02 None

你可以使用你的堆栈跟踪共享吗？ – 2015-04-02 04:26:25

ArrayList变量transList为空。你需要在构造函数初始化：

public CheckingAccount(double initialVal) { 
    balance = initialVal; 
    totalServiceCharge = 0; 
    transCount = 0; 
    transList = new ArrayList<Transaction>();//here 
}

来源

2015-04-02 04:42:55 Arvind

你很快，我回答同样的！：p – Sarz 2015-04-02 04:44:14

非常感谢您的帮助 – None 2015-04-03 05:07:16

@无，很高兴它帮助了您，现在您可以接受我的答案。 – Arvind 2015-04-03 10:18:00

空指针异常就要来了，因为你还没有创建了一个ArrayList对象添加。

在“public CheckingAccount（double initialVal）”构造函数中插入以下行。

transList = new ArrayList<Transaction>();

参考：每当出现空指针异常时，检查赋值对象是否已经可用。

来源

2015-04-02 04:44:09

使用GUI的Java空指针异常错误

回答

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