因此，我正在编写一个使用GUI模仿支票帐户的程序。我的功能之一有问题。我创建了一个Transaction对象，并调用了一个支票帐户中的函数，以将该交易帐户添加到checkingaccount类中的Transaction数组列表中。但是，每次调用该函数时，我都会收到空指针异常错误。我怎样才能解决这个问题？
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);
}
}
提前致谢。
最佳答案
ArrayList变量transList为空。您需要在构造函数中对其进行初始化：
public CheckingAccount(double initialVal) {
balance = initialVal;
totalServiceCharge = 0;
transCount = 0;
transList = new ArrayList<Transaction>();//here
}