这是我第一次学习java，也是第一次上网站。这是我们的 3 个最终项目之一，我碰壁了，我有两个星期的时间来做这个，我无法显示总数。
任务是使用 GUI 的表示类和具有所有计算的帐户类创建一个银行帐户。在演示类中，我们创建了 3 个面板：第一个面板包含 3 个单选按钮，一个用于创建帐户，一个用于进行交易（存款或取款），第三个按钮显示所有帐户
在第二个面板中，客户首先必须创建一个帐户，输入他们的名字姓氏和密码。然后，textArea 将显示初始余额为 100 美元的输入信息。我对此没有意见。![面板][1]
在第三个面板中，客户可以选择是否要存款或取款，然后输入金额。我们必须创建一个可以计算至少 10 个帐户的数组。如果他们想要进行交易，则必须检查数组是否有重复的 pin，如果没有重复，则 TextArea 将显示 pin、名称、交易类型、交易金额和余额。
这就是我的问题所在，我不确定我是否正确检查了重复的引脚，当我尝试显示时，我得到一个空指针异常。任何关于我做错了什么的方向或建议都可能真的很有帮助。先感谢您。
演示类：
我的问题出在方法 findPin2Duplicate() 和显示 transactions() 中。不确定是不是因为 find2Duplicate() 而没有显示，还是因为它也有问题。
import javax.swing.*; //needed for swing components
import java.awt.*; //needed for ItemListener and ActionListener interfaces
import java.awt.event.*; //needed for Font class
import java.text.DecimalFormat;
public class Presentation extends JFrame
implements ActionListener
{
//Declare components
JLabel titleLabel = new JLabel("The Friendly NeighborHood Bank");
//intro panel
JRadioButton createAccountRadioButton = new JRadioButton("Create New Account");
JRadioButton transactionRadioButton = new JRadioButton("Deposit or Withdrawal");
JRadioButton displayRadioButton = new JRadioButton("Display all accounts");
JRadioButton default1RadioButton = new JRadioButton();
ButtonGroup introButtonGroup = new ButtonGroup();
//new account panel
JTextField firstNameTextField = new JTextField (20);
JTextField lastNameTextField = new JTextField(20);
JTextField pin1TextField = new JTextField(20);
JTextArea output1TextArea = new JTextArea(18,45);
JButton process1Button = new JButton ("Process");
JButton back1Button = new JButton ("Back");
//deposit or withdrawal panel
JRadioButton depositRadioButton = new JRadioButton("Deposit");
JRadioButton withdrawalRadioButton = new JRadioButton("Withdrawal");
JRadioButton default2RadioButton = new JRadioButton();
ButtonGroup transactionButtonGroup = new ButtonGroup();
JTextField pin2TextField = new JTextField(20);
JTextField amountTextField = new JTextField(20);
JTextArea output2TextArea = new JTextArea(20,30);
JButton process2Button = new JButton ("Process");
JButton back2Button = new JButton ("Back");
JScrollPane outputScrollPane1 = new JScrollPane(output1TextArea);
JScrollPane outputScrollPane2 = new JScrollPane(output2TextArea);
Font plainFont = new Font("Times New Roman", Font.PLAIN, 14);
Font taFont = new Font("Courier", Font.PLAIN, 12);
JPanel introPanel = new JPanel();
JPanel newAccountPanel = new JPanel();
JPanel transactionPanel = new JPanel();
//declare instance variables
Account myAccountArray[] = new Account[10];
int lastAccountInteger = -1;
int pinIndexInteger = 0;
public static void main(String[] args)
{
// This method creates sets the default close operation
Presentation myProgram = new Presentation();
myProgram.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}//end of main method
//This is the constructor and will call the 3 panels to add the components to the GUI,
//register the listeners, and set the properties of the JFrame
public Presentation()
{
super("Account");
//Constructor - calls methods to add components to panel, set up
//the listeners, and set properties for the JFrame
introPanel();
newAccountPanel();
transactionPanel();
//Call method to add controls and set listeners
addListeners();
//add the intro panel to the frame and set the size and the visibility of the frame
add(introPanel);
setSize(200,300);
setVisible(true);
}
// This method will add components to the first panel shown
public void introPanel()
{
introButtonGroup.add(createAccountRadioButton);
introButtonGroup.add(transactionRadioButton);
introButtonGroup.add(displayRadioButton);
introButtonGroup.add(default1RadioButton);
createAccountRadioButton.setSelected(false);
transactionRadioButton.setSelected(false);
displayRadioButton.setSelected(false);
default1RadioButton.setSelected(true);
introPanel.add(titleLabel);
introPanel.add(createAccountRadioButton);
introPanel.add(transactionRadioButton);
introPanel.add(displayRadioButton);
}
//This method will add components to a second panel
public void newAccountPanel()
{
newAccountPanel.add(titleLabel);
newAccountPanel.add(new JLabel("First Name:"));
newAccountPanel.add(firstNameTextField);
newAccountPanel.add(new JLabel("Last Name:"));
newAccountPanel.add(lastNameTextField);
newAccountPanel.add(new JLabel("PIN:"));
newAccountPanel.add(pin1TextField);
output1TextArea.setFont(taFont);
String formattedTitleString = String.format("%-10s%13s%15s%n", "Name",
"PIN", "Balance");
output1TextArea.append(formattedTitleString);
newAccountPanel.add(output1TextArea);
newAccountPanel.add(new JLabel(" Programmed by: Maria Garcia "));
newAccountPanel.add(process1Button);
newAccountPanel.add(back1Button);
}
//This method will add components to a third panel
public void transactionPanel()
{
transactionButtonGroup.add(depositRadioButton);
transactionButtonGroup.add(withdrawalRadioButton);
transactionButtonGroup.add(default2RadioButton);
depositRadioButton.setSelected(false);
withdrawalRadioButton.setSelected(false);
default2RadioButton.setSelected(true);
transactionPanel.add(titleLabel);
transactionPanel.add(depositRadioButton);
transactionPanel.add(withdrawalRadioButton);
transactionPanel.add( new JLabel ("PIN:"));
transactionPanel.add(pin2TextField);
transactionPanel.add(new JLabel ("Amount:"));
transactionPanel.add(amountTextField);
output2TextArea.setFont(taFont);
String formattedTitleString = String.format("%-8s%11s%13s%11s%13s%n", "PIN",
"Name", "Transaction Type ", "Transaction Amount", "Balance");
output2TextArea.setText(formattedTitleString);
transactionPanel.add(output2TextArea);
transactionPanel.add(new JLabel(" Programmed by: Maria Garcia "));
transactionPanel.add(process2Button);
transactionPanel.add(back2Button);
}
public void addListeners()
{
//This method sets up the listeners
//radio buttons set up to respond to the ItemListener
process1Button.addActionListener(this);
back1Button.addActionListener(this);
process2Button.addActionListener(this);
back2Button.addActionListener(this);
amountTextField.addActionListener(this);
createAccountRadioButton.addActionListener(this);
transactionRadioButton.addActionListener(this);
displayRadioButton.addActionListener(this);
depositRadioButton.addActionListener(this);
withdrawalRadioButton.addActionListener(this);
}//end of addListeners method
public void actionPerformed(ActionEvent evt)
{
Object sourceObject = evt.getSource();
if(sourceObject == createAccountRadioButton)
{
if(createAccountRadioButton.isSelected())
{
remove(introPanel);
default1RadioButton.setSelected(true);
remove(transactionPanel);
add(newAccountPanel);
setSize(420,475);
setVisible(true);
}
} //to display the admin panel
else if(sourceObject == transactionRadioButton )
{
if(transactionRadioButton.isSelected())
{
remove(introPanel);
default2RadioButton.setSelected(true);
remove(newAccountPanel);
add(transactionPanel);
setSize(420,500);
setVisible(true);
}
}
if(sourceObject == process1Button)
{
if(newAccountValidation() == true) // validation method will be called and then the processRental
{
displayNewAccount();
}
}
else if (sourceObject ==process2Button )
{
if(transactionsValidation() == true)
{
if(findPin2Duplicate()== false)
{
displayTransactions();
//reset();
}
}
}
else if ( sourceObject == back1Button) //If the summary button is pressed then the summary method will be called
{
remove(newAccountPanel);
add(introPanel);
setSize(200,300);
setVisible(true);
}
else if (sourceObject == back2Button)
{
remove(transactionPanel);
add(introPanel);
setSize(200,300);
setVisible(true);
}
else if (displayRadioButton.isSelected())
{
summary();
}
}
public boolean newAccountValidation()
{
boolean newAccountValidationBoolean;
if(!(firstNameTextField.getText()).equals(""))
{
if(!(lastNameTextField.getText()).equals(""))
{
if (!(pin1TextField.getText()).equals(""))
{
newAccountValidationBoolean = true;
}
else
{
JOptionPane.showMessageDialog(null, "Please enter your pin");
pin1TextField.requestFocus();
newAccountValidationBoolean = false;
}
}
else
{
JOptionPane.showMessageDialog(null, "Please enter your last name");
lastNameTextField.requestFocus();
newAccountValidationBoolean = false;
}
}
else
{
JOptionPane.showMessageDialog(null, "Please enter your first name");
firstNameTextField.requestFocus();
newAccountValidationBoolean = false;
}
return newAccountValidationBoolean;
}
public boolean transactionsValidation()
{
boolean transactionsValidationBoolean;
if(!(pin2TextField.getText()).equals(""))
{
if(!(amountTextField.getText()).equals(""))
{
transactionsValidationBoolean = true;
}
else
{
JOptionPane.showMessageDialog(null, "Please enter an amount");
amountTextField.requestFocus();
transactionsValidationBoolean = false;
}
}
else
{
JOptionPane.showMessageDialog(null, "Please enter your pin");
pin2TextField.requestFocus();
transactionsValidationBoolean = false;
}
return transactionsValidationBoolean;
}
public void displayNewAccount()
{
String firstNameString = ("");
String lastNameString = ("");
String pinString = ("");
DecimalFormat valueDecimalFormat = new DecimalFormat("$#0.00");
if (lastAccountInteger >= 0) //don't want to do this for the first account
{
if(findPin1Duplicate() == false)
{
lastAccountInteger ++;
myAccountArray[lastAccountInteger]= new Account(firstNameString, lastNameString, pinString);
String nameString = lastNameTextField.getText() + ", " + firstNameTextField.getText();
double Amount = (myAccountArray[lastAccountInteger].getBalance());
String tempString1 = Double.toString(Amount);
output1TextArea.append(nameString + "\t " + pin1TextField.getText() + "\t " + "$" + tempString1 + "\n");
//String formattedOutputString = String.format("%6s%9s%13s%n", nameString, myAccountArray[lastAccountInteger].getTransactionAmount(transactionAmountDouble));
//myAccountArray[lastAccountInteger].getPin();
//output1TextArea.append(formattedOutputString);
}
else
{
String displayString = "Enter a valid Pin";
JOptionPane.showMessageDialog(null, displayString);
}
//JOptionPane message
}
else
{
lastAccountInteger ++;
myAccountArray[lastAccountInteger]= new Account(firstNameString, lastNameString, pinString);
String nameString = lastNameTextField.getText() + ", " + firstNameTextField.getText();
double Amount = (myAccountArray[lastAccountInteger].getBalance());
String tempString1 = Double.toString(Amount);
output1TextArea.append(nameString + "\t " + pin1TextField.getText() + "\t " + "$" + tempString1 + "\n");
}
}
public void displayTransactions()
{
String firstNameString = ("");
String lastNameString = ("");
String pinString = ("");
char typeOfTransactionChar = (' ');
String transactionString = ("");
double transactionAmountDouble = 0.0;
double amountDouble = 0.0;
//for (int i = 0; i < lastAccountInteger; i++)
lastAccountInteger++;
myAccountArray[lastAccountInteger]= new Account(firstNameString, lastNameString, pinString);
if (lastAccountInteger >= 0)
{
if (depositRadioButton.isSelected())
{
amountDouble =myAccountArray[lastAccountInteger].getDeposit();
//typeOfTransactionChar ='D';
transactionString = "Deposit";
//transactionAmountDouble = depositAmountDouble ;
}
else if( withdrawalRadioButton.isSelected())
{
amountDouble = myAccountArray[lastAccountInteger].getWithdrawal();
//typeOfTransactionChar= 'W';
transactionString = "Withdrawal";
//transactionAmountDouble = withdrawalAmountDouble;
}
}
String nameString = lastNameTextField.getText() + ", " + firstNameTextField.getText();
String tempString = Double.toString(amountDouble);
output2TextArea.append(pinString + nameString + transactionString + amountDouble);
//String formattedTransactionString = String.format("%-10s%6s%9s%9s%13s%11s%n", transactionString); //6d=decimal integer
// output2TextArea.append(formattedTransactionString);
}
public boolean findPin1Duplicate()
{
boolean itemFoundBoolean = false;
pinIndexInteger = 0;
String listItemString;
lastAccountInteger++;
String pinString = myAccountArray[lastAccountInteger].getPin();
String inputPin1String = pin1TextField.getText();
int arrayPin1Sum = 0;
while (!itemFoundBoolean && pinIndexInteger < lastAccountInteger)
{
//listItemString = String.valueOf(arrayPin1Sum);
if(inputPin1String.equalsIgnoreCase(pinString))
{
itemFoundBoolean = true;
}
else
pinIndexInteger++;
}
return itemFoundBoolean;
}
public boolean findPin2Duplicate()
{
boolean itemFoundBoolean = false;
pinIndexInteger = 0;
lastAccountInteger ++;
String pin2String = myAccountArray[lastAccountInteger].getPin();
String inputPin1String = pin2TextField.getText();
int arrayPin2Sum = 0;
// for (int i = 0; i < myAccountArray.length; i++)
//{
//pin2String += myAccountArray[i].getPin();
//}
while (!itemFoundBoolean && pinIndexInteger < lastAccountInteger)
{
//listItemString = String.valueOf(arrayPin2Sum);
if(inputPin1String.equalsIgnoreCase(pin2String))
{
itemFoundBoolean = true;
}
else
{
pinIndexInteger++;
}
}
return itemFoundBoolean;
}
//method to display summary
public void summary()
{
//Format the values to currency format
DecimalFormat valueDecimalFormat = new DecimalFormat("$#0.00");
}
//This method resets the textfields for re-entry and sends the cursor to the nameTextField
public void reset()
{
} //end of reset method
}
Account Class
public class Account
{
//declare instance variables
//constants
private final double DEPOSIT_AMOUNT_DOUBLE = 100.0;
//class variables
private double withdrawalAmountDouble;
private static double currentBalanceDouble;
private double totalAmountDouble;
private static double totalCount;
private static double totalDepositDouble;
private double depositAmountDouble;
private static String firstNameString;
private static String lastNameString;
private static String fullNameString;
private static String pinString;
private static double addedAmountDouble;
private static String transactionTypeString;
private static boolean balanceBoolean;
private static char typeOfTransactionChar;
private static double transactionAmountDouble;
private static double totalWithdrawalAmountDouble;
private static double totalDepositAmountDouble;
private static double grossTransactionDouble;
private static double balanceDouble;
private static boolean isValidBoolean;
//Constructors
public Account()
{
setFirstName("");
setLastName("");
setPin("");
totalCount++;
}
public Account(String newFirstNameString, String newLastNameString, String newPinString)
{
setFirstName(newFirstNameString);
setLastName(newLastNameString);
setPin(newPinString);
setBalance(DEPOSIT_AMOUNT_DOUBLE);
}
public void setFirstName(String newFirstNameString)
{
firstNameString = newFirstNameString;
}
public void setLastName(String newLastNameString)
{
lastNameString = newLastNameString;
}
public void setPin(String newPinString)
{
pinString = newPinString;
}
//this method will set the type of transaction for the transaction panel
public void setBalance(double newBalanceDouble)
{
balanceDouble = newBalanceDouble;
}
public String getTypeOfTransaction()
{
return transactionTypeString;
}
public double getBalance()
{
return balanceDouble;
}
public double getTransactionAmountDouble()
{
return transactionAmountDouble;
}
public double getTransactionAmount(double newTransactionAmountDouble)
{
currentBalanceDouble = DEPOSIT_AMOUNT_DOUBLE;
transactionAmountDouble = currentBalanceDouble;
return transactionAmountDouble;
}
public String getFirstNameString()
{
return firstNameString;
}
public String getLastNameString()
{
return lastNameString;
}
public void setName()
{
fullNameString = (firstNameString + " , " + lastNameString);
}
public String getName()
{
return fullNameString;
}
public void setIsValid(double newBalanceDouble)
{
if (balanceDouble > currentBalanceDouble)
{
isValidBoolean = false;
}
}
public void setDeposit(double newDepositDouble)
{
balanceDouble += newDepositDouble;
}
public void setWithdrawal(double newWithdrawalDouble)
{
balanceDouble -= (newWithdrawalDouble);
}
public double getDeposit()
{
return balanceDouble;
}
public double getWithdrawal()
{
return balanceDouble;
}
public boolean getIsValid()
{
return isValidBoolean;
}
public String getPin()
{
return pinString;
}
}
再次感谢任何可以引导我走向正确方向或指出我的错误的地方。先感谢您