帮助！我不太了解java，但我试图创建一个小程序，人们可以购买物品，股票应根据他们的购买更新。我有两个不同的类，但我想要做的是，我想获得用户从一个类购买的项目数量，并使用该数字更新另一个类中的股票 - 这是我的代码部分，我是
挣扎采购项目代码
public class PurchaseItem extends JFrame implements ActionListener {
JTextField ItemNo = new JTextField(5); //Adds a text field named ItemNo
JTextField AmountNo = new JTextField(5); //Adds a text field named AmountNo
TextArea information = new TextArea(6, 40); //Adds a text area named Information
TextArea reciept = new TextArea (10,50); //Adds a text area named Reciept
JButton Check = new JButton("Check"); //Adds a button named Check
JButton Buy = new JButton("Buy"); //Adds a button named Buy
DecimalFormat pounds = new DecimalFormat("£#,##0.00"); //For output to display in decimal and pounds format
public PurchaseItem() { //PurchaseItem class
this.setLayout(new BorderLayout()); //Adds a new layout for PurchaseItem
JPanel top = new JPanel(); //JPanel is a a container for other components
top.setLayout(new FlowLayout(FlowLayout.CENTER)); //It is set to the center of the frame
JPanel bottom = new JPanel(); //JPanel is a a container for other components
bottom.setLayout(new FlowLayout(FlowLayout.CENTER)); //It is set to the center of the frame
bottom.add(Buy); //Insert the "Buy" JButton on the frame
this.add(bottom, BorderLayout.SOUTH); //Button goes at the bottom of the frame
setBounds(100, 100, 450, 250); //Sets the bounds of the frame
setTitle("Purchase Item"); //Sets the title of the frame
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); //Default option to exit frame is through button and not X sign
top.add(new JLabel("Enter Item Key:")); //Add a new JLabel at the top of the frame
top.add(ItemNo); //Set the ItemNo Text Field at the top of the frame
top.add(new JLabel ("Enter Amount:")); //Add a new JLabel at the top of the frame
top.add(AmountNo); //Set the AmountNo Text Field at the top of the frame
top.add(Check); //Set the Check Button at the top of the frame
Buy.setText("Buy"); Buy.setVisible(true); //Makes the text of the Buy Button visible
Check.addActionListener(this); //Add an ActionListener to the Check Button
Buy.addActionListener(this); //Add an ActionListener to the Buy Button
add("North", top);
JPanel middle = new JPanel(); //JPanel is a a container for other components
middle.add(information); //Set the Information Text Area at the middle of the frame
add("Center", middle);
setResizable(false); //Makes the frame not resizeable
setVisible(true); //Makes the frame visible
}
@Override //Overrides the method of the PurchaseItem class to identify mistakes and typos
public void actionPerformed(ActionEvent e) { //actionPerformed class. This is called when the actionListener event happens
String ItemKey = ItemNo.getText(); //String for getting the user input from the ItemNo Text Field
String ItemAmount = AmountNo.getText(); //String for getting the user input from the AmountNo Text Field
String Name = StockData.getName(ItemKey); //String for getting the name of the item from StockData
int Amount = Integer.parseInt(ItemAmount); //Convert String ItemAmount into an Integer variable named Amount
int NewStock = StockData.getQuantity(ItemKey) - Amount; //Integer named NewStock. NewStock is the current stock(from StockData) minus the Amount
double Total = Amount * StockData.getPrice(ItemKey); //Double named Total. Total is the Amount multiplied by the price of the item(from StockData)
Calendar cal = Calendar.getInstance(); //Calendar named cal. getInstance is used to get the current time
SimpleDateFormat Date = new SimpleDateFormat("dd/MM/yyyy"); //SimpleDateFormat named Date. It is used to display the date
SimpleDateFormat Time = new SimpleDateFormat("HH:mm:ss"); //SimpleDateFormat named Time. It is used to display the time
if (Name == null){ //If the Name is invalid and has no return value
information.setText("There is no such item"); //Display the message on the Information Text Area
}
else if (Amount > StockData.getQuantity(ItemKey)) { //Else if the Amount(User Input) is more than the quantity of the item(from StockData)
information.setText("Sorry there is not enough stock available"); //Display the message on the Information Text Area
}
else { //Otherwise
information.setText(Name + " selected: " + Amount); //Add the Name and the Amount of the item on the Information Text Area
information.append("\nIndividual Unit Price: " + pounds.format(StockData.getPrice(ItemKey))); //On a new line add the individual price of the item on the Information Text Area in a pound format(£)
information.append("\nCurrent Stock Available: " + StockData.getQuantity(ItemKey)); //On a new line add the current quantity available according to StockData on the Information Text Area
information.append("\nNew Stock After Sale: " + NewStock); //On a new line add the NewStock on the Information Text Area
information.append("\n\nTotal: " + Amount + " Units" + " at " + pounds.format(StockData.getPrice(ItemKey)) + " each"); //On two new lines add the Amount plus the item price(from StockData). This becomes the Total
information.append("\n= " + pounds.format(Total)); //On a new line display the Total in a pounds format(£) on the Information Text Area
}
if (e.getSource() == Buy) { //If the user clicks the Buy Button
int response = JOptionPane.showConfirmDialog(null, "Buy " + Amount + " Units" + " for " + pounds.format(Total) + "?"); //Show a confirm dialog asking the user to confirm the purchase with a Yes, No, or Cancel option
if (response == JOptionPane.YES_OPTION) { //If the user clicks Yes on the confirm dialog
JFrame frame2 = new JFrame(); //Add a new JFrame called frame2
TextArea Reciept = new TextArea ("Receipt For Your Purchase", 20,40); //Add the Receipt Text Area onto frame2 and show the message
Reciept.append("\n\nTime: " + Time.format(cal.getTime())); Reciept.append("\nDate: " + Date.format(cal.getTime())); //On seperate lines add the Time and the Date (from Calendar)
Reciept.append("\n\nYou Have Purchased The Following Item(s): "); //Display the message
Reciept.append("\n\n" + Name + "\n" + Amount + " Units" + "\n" + pounds.format(StockData.getPrice(ItemKey)) + " each"); //On a line add the Name and Item Amount followed by the item price (from StockData) on a new line
Reciept.append("\n\n\n" + Amount + " Unit(s)" + " at " + pounds.format(StockData.getPrice(ItemKey)) + " each" + "\nTotal = " + pounds.format(Total)); //After 3 lines display the Item Amount and the item price on the same line. On a new line display the Total in a pounds format
Reciept.append("\n\n\nThank You For Your Purchase" + "\n\nGoodbye :)"); //Show a message on two seperate lines
frame2.pack(); frame2.setSize(375, 380); frame2.setLocation(250, 250); ;frame2.setTitle("Receipt"); //Sets the size, the location, and the title of frame2
frame2.setVisible(true); frame2.setResizable(false); //sets frame2 so that it is visible and not resizable
frame2.add(Reciept); //Display the Reciept Text Area on frame2
frame2.setLayout(new FlowLayout(FlowLayout.CENTER)); //It is set to the center of the frame
}else{ //Otherwise
if (response == JOptionPane.NO_OPTION){ //If the user clicks No or Cancel on the confirm dialog
//Do nothing
}
}
检查库存的代码
public class CheckStock extends JFrame implements ActionListener {
JTextField stockNo = new JTextField(7); //adds a text field for user input
JTextField AmountNo = new JTextField(5);
TextArea information = new TextArea(6, 40); //adds a text area for the output
JButton check = new JButton("Check Stock"); //adds a button with the text "Check Stock"
JButton Clear = new JButton();
DecimalFormat pounds = new DecimalFormat("£#,##0.00"); //for output to display in decimal and pound format
public CheckStock() { //"CheckStock" class
setLayout(new BorderLayout()); //adds a new frame for "CheckStock"
setBounds(100, 100, 450, 220); //sets the size and location of the frame
setTitle("Check Stock"); //sets the title of the frame
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); //user has to click on "Exit" button instead of X sign
check.addActionListener(this); //adds an action listener for the "check" button so when clicked by user, "actionPerformed" class is called
JPanel top = new JPanel(); //JPanel is a a container for other components. It is used at the top of the frame
add("North", top);
top.add(new JLabel("Enter Item Key:")); //adds a label at the top of tne frame
top.add(stockNo); //adds the "stockNo" text field to the top of the frame
top.add(check); //adds the "check" button to the top of the frame
JPanel middle = new JPanel(); //JPanel is a a container for other components. It is used at the middle of the frame
add("Center", middle);
middle.add(information); //in the middle of the frame, add the "information" text area
setResizable(false); //frame is not resizable
setVisible(true); //frame is visible
}
public void actionPerformed(ActionEvent e) { //this code is fired once the user runs the ActionListener
String key = stockNo.getText(); //string named "key" for the stockNo
String name = StockData.getName(key); //string named "name" for the stockData
int Quantity = StockData.getQuantity(key);
int NewStock;
if (name == null) { //if there is no input in the text field
information.setText("Enter Item Key"); //display the message on the text area
}
else if (e.getSource() == check) {
StockData.getQuantity(key);
information.append( "" + StockData.getName(key));
information.append("\n New Stock: " + StockData.getQuantity(key)); //otherwise
information.setText(name); //display the name of the item
information.append("\nPrice: " + pounds.format(StockData.getPrice(key))); //display the price of the item using pound format
information.append("\nPrevious Stock: " + Quantity); //display the amount in stock for the item according to StockData
}
}
}
答案 0 :(得分：0)
您没有初始化对象Update：您的代码行应该是
PurchaseItem Update = new PurchaseItem();
（另一点我看不到任何代码将你创建的JComponent（例如按钮，文本字段......）添加到相应类的两个框架或显示两个框架;如果是不包含在您的代码中，请务必添加这些代码片段）。
最后，如果您需要一个代码来检查Updated值的变化，这里是您可以使用的最简单（但不是唯一）的技术，创建一个线程（请参阅Oracle documentation以了解什么是线程以及如何使用它们：
int refreshTime = 1000; // Refresh time in milliseconds
boolean running = true; // Set it to false if you want to stop the thread
Runnable r = new Runnable({
@Override
public void run() {
while(running) {
Thread.sleep(refreshTime);
// Put here your code to update your frames or your variables
}
});