无法运行 string.format + 退出按钮问题

Question

我正在做我的第一个项目。当我试图转到新行时，string.format它以某种方式失败了（要么根本不打印，要么在同一行打印）。这是代码：    String reciept = String.format("Recipt number #16424 +"  + "%n" + "Beef Burgers :" + ab1 +"%n" + "Cheese Burgers :" + ab2 + "%n" +   "Fish and Chips :" + ab3 + "%n"  + "French Fries :" + ab5 + "%n" +  "Steak :" + ab4 + "%n"  + "Sprite Drinks : " + ab + "%n" +  "Soda Drinks : " + ab8 + "%n" + "Fuzetea Drinks : " + ab7 + "%n" + "Coke Drinks :" + ab6 + "%n" , ab,ab1,ab2,ab3,ab4,ab5,ab6,ab7,ab8);            recieptText.setText(reciept);还有 1 个问题。我正在尝试创建JButton出口。我试图打开一条消息，说如果我确定退出然后退出，但我失败了，所以我尝试了注册，如果他按下退出，它将退出，我也失败了。JButton btnExit = new JButton("Exit");btnExit.setFont(new Font("Tahoma", Font.PLAIN, 19));btnExit.setBounds(766, 484, 127, 39);if (btnExit.isSelected()==true) {    System.exit(0);}frame.getContentPane().add(btnExit);

Answer 1

雪，你正处于一段漫长而有趣且富有成果的旅程的开始。祝你好运！对于您的第一个问题，就面向对象设计原则而言，在不同的完善水平上有许多正确的答案。我需要建议你尽早阅读 Java 编码标准、控制反转、单元测试。我将仅提及封装并推荐您以下解决方案。

我将首先创建两个类 Receipt 和 ReceiptItem（可以根据项目的范围创建 Product、ProductPrice 等），假设它不仅是您尝试打印的单个收据（并且可能用于存储收据以供以后检查）还需要一个持久层，这是为您探索的另一个领域），但您将处理许多带有更多收据详细信息行的收据。然后我将创建这两个类的实例，并在将其发送到文本显示/打印设备之前调用 Receipt 类的 toFormattedString 方法。

public class ReceiptItem {

    private static final int TITLE_WIDTH = 30;

    private static final String DETAIL_FORMAT="%-" + TITLE_WIDTH + "s : %6s%n";

    private String title;

    private BigDecimal totalPrice;

    public ReceiptItem(String title, BigDecimal totalPrice) {

        setTitle(title);

        setTotalPrice(totalPrice);

    }

    public String getTitle() {

        return title;

    }

    public void setTitle(String title) {

        this.title = title;

    }

    public BigDecimal getTotalPrice() {

        return totalPrice;

    }

    public void setTotalPrice(BigDecimal totalPrice) {

        this.totalPrice = totalPrice;

    }

    public String toFormattedString() {

        return String.format(DETAIL_FORMAT, getTitle(),

                getTotalPrice().toPlainString());

    }

}

public class Receipt {

    private static final String RECEIPT_HEADER_FORMAT = "Receipt number #%s%n";

    private static int LAST_RECEIPT_NUMBER = 0;

    private int receiptNumber;

    private List<ReceiptItem> items= new ArrayList<>();

    public Receipt() {

        super();

        setReceiptNumber(++LAST_RECEIPT_NUMBER);

    }

    public Receipt(int receiptNumber) {

        this();

        setReceiptNumber(LAST_RECEIPT_NUMBER=receiptNumber);

    }

    public void addItem(ReceiptItem item) {

        items.add(item);

    }

    public int getReceiptNumber() {

        return receiptNumber;

    }

    public void setReceiptNumber(int receiptNumber) {

        this.receiptNumber = receiptNumber;

    }

    public List<ReceiptItem> getItems() {

        return items;

    }

    public void setItems(List<ReceiptItem> items) {

        this.items = items;

    }

    public String toFormattedString() {

        StringBuilder builder = new StringBuilder();

        builder.append(String.format(RECEIPT_HEADER_FORMAT, getReceiptNumber()));

        for (ReceiptItem item:getItems()) {

            builder.append(item.toFormattedString());

        }

        return builder.toString();

    }

}

Receipt receipt = new Receipt();

receipt.addItem(new ReceiptItem("Beef Burgers", new BigDecimal("5.00")));

receipt.addItem(new ReceiptItem("Cheese Burgers", new BigDecimal("5.00")));

receipt.addItem(new ReceiptItem("Fish and Chips", new BigDecimal("6.00")));

receipt.addItem(new ReceiptItem("French Fries", new BigDecimal("4.00")));

receipt.addItem(new ReceiptItem("Steak", new BigDecimal("10.00")));

receipt.addItem(new ReceiptItem("Sprite Drinks", new BigDecimal("1.00")));

receipt.addItem(new ReceiptItem("Soda Drinks", new BigDecimal("0.40")));

receipt.addItem(new ReceiptItem("Fuzetea Drinks", new BigDecimal("0.70")));

recieptText.setText(reciept.toFormattedString());

我对你的第二个问题的回答：

JFrame frame = new JFrame();

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

//... Your code here

JButton btnExit = new JButton("Exit");

btnExit.setFont(new Font("Tahoma", Font.PLAIN, 19));

btnExit.setBounds(766, 484, 127, 39);

if (btnExit.isSelected()==true) {

    System.exit(0);

}

btnExit.addActionListener((e)-> {

    int confirm = JOptionPane.showOptionDialog(frame,

            "Are You Sure to Close this Application?",

            "Exit Confirmation", JOptionPane.YES_NO_OPTION,

            JOptionPane.QUESTION_MESSAGE, null, null, null);

    if (confirm == JOptionPane.YES_OPTION) {

        System.exit(0);

    }

});

frame.getContentPane().add(btnExit);

frame.addWindowListener(new WindowAdapter() {

    @Override

    public void windowClosing(WindowEvent e) {

        int confirm = JOptionPane.showOptionDialog(frame,

                "Are You Sure to Close this Application?",

                "Exit Confirmation", JOptionPane.YES_NO_OPTION,

                JOptionPane.QUESTION_MESSAGE, null, null, null);

        if (confirm == JOptionPane.YES_OPTION) {

            System.exit(0);

        }

    }

});

frame.setVisible(true);

frame.pack();