Question

关于以下代码 - 如果在添加图书时将“数字”以外的任何内容输入“成本”，我正试图将其抛出和异常，因为您可以看到我已经做到了这样做但我只是想要显示一个消息对话框，指出“请输入一个数字”，而不是出现输入对话框，当我尝试更改为消息对话框时Eclipse返回错误。有什么建议吗？

相关摘录

do{
        try { 
            cost = Double.parseDouble(JOptionPane.showInputDialog("Cost"));
            book.setCost(cost);
            goodInput = true;
            } 
            catch (NumberFormatException nfe){ 
            cost = Double.parseDouble(JOptionPane.showInputDialog ("Numerical entry expected. Please try again"
            )); 
            } 
        }while (!goodInput);

这是完整的代码。感谢。

import java.awt.FlowLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import javax.swing.*;

import java.awt.event.ActionListener; 
import java.util.ArrayList;

public class BookGUI extends JFrame implements ActionListener

{

    //String addBook="";
    // public ArrayList<Book> books;

    //Book books = new Book ("", "", 0, "", 0);
    Book book = new Book("", "", 0, "", 0);
    String title  = "";
    String author  = "";
    int year = 0;
    String publisher  = "";
    double cost = 0;
    double total = 0;
    boolean goodInput = false;


    public BookShelf bookShelf = new BookShelf();
    public static final int WIDTH = 300;
    public static final int HEIGHT = 200;

    //Creates & displays a window of the class FlowLayoutDemo
    public static void main(String[] args)
    {
        BookGUI gui = new BookGUI( );
        gui.setVisible(true);
    }

   // public String getTitle()
   // {
    //    return title;
    //}

    public void setTitle(String title) //this is relevant
    {
        this.title = title;
    }

    public void setAuthor(String author) //this is relevant
    {
        this.author = author;
    }

    public void setYear(int year) //this is relevant
    {
        this.year = year;
    }
    public void setPublisher(String publisher) //this is relevant
    {
        this.publisher = publisher;
    }

    public void setCost(double cost) //this is relevant
    {
        this.cost = cost;
    }

    public BookGUI( )
    {

        setSize(WIDTH, HEIGHT);
        addWindowListener(new WindowDestroyer( ));
        setTitle("GUI Assignment");
        Container content = getContentPane( );

        content.setLayout(new FlowLayout());

        JButton button1 = new JButton("Hightest Price Paid");
        content.add(button1);
        button1.addActionListener(this);
        //contentPane.add(button1);

        JButton button2 = new JButton("Cost of BookShelf");
        content.add(button2);
        button2.addActionListener(this);

        JButton button3 = new JButton("Size of BookShelf");
        content.add(button3);
        button3.addActionListener(this);

        JButton button4 = new JButton("Add Book");
        content.add(button4);
        button4.addActionListener(this);     

    }

    public void actionPerformed(ActionEvent e)
    {
        if (e.getActionCommand().equals("Add Book"))
       //book = JOptionPane.showInputDialog("Add Book");
        {     //set up the book object with all the data passed in
        title = JOptionPane.showInputDialog("Title");
        author = JOptionPane.showInputDialog("Author");
        publisher = JOptionPane.showInputDialog("Publisher");
        //cost = JOptionPane.showInputDialog("Cost");
        //cost = Double.parseDouble(JOptionPane.showInputDialog("Cost"));
        do{
        try { 
            cost = Double.parseDouble(JOptionPane.showInputDialog("Cost"));
            book.setCost(cost);
            goodInput = true;
            } 
            catch (NumberFormatException nfe){ 
            cost = Double.parseDouble(JOptionPane.showInputDialog ("Numerical entry expected. Please try again"
            )); 
            } 
        }while (!goodInput);


        book.setTitle(title);
        book.setAuthor(author);
        book.setPublisher(publisher);
        bookShelf.addBook(book);

        String message =  "The title of the book is :" + title + 
        "the Author of the Book is : " + author + " and it's published by " + publisher + "and it costs" + cost + "euro";
        JOptionPane.showMessageDialog(null, message, "Book Details", JOptionPane.PLAIN_MESSAGE);
        }
        else if (e.getActionCommand().equals("Size of BookShelf")) {
            int sizeOfBookShelf = bookShelf.sizeOfBookshelf();
            String message = "The book shelf has " + sizeOfBookShelf + " book(s)";
            JOptionPane.showMessageDialog(this, message);
        }
        else if (e.getActionCommand().equals("Cost of BookShelf")) 
        {
            double costOfBookshelf = bookShelf.costOfBookShelf();
            String message = "The book shelf value is " + total + costOfBookshelf + "Euro";
            JOptionPane.showMessageDialog(this, message);
        }

    }
    }

Answer 1

当发生异常时，您不应该尝试阅读用户在消息对话框中输入的内容：消息对话框并不意味着输入任何内容。这就是showMessageDialog返回void的原因，而不是像showInputDialog那样的String。取代

catch (NumberFormatException nfe){ 
        cost = Double.parseDouble(JOptionPane.showInputDialog ("Numerical entry expected. Please try again"
        ));

与

catch (NumberFormatException nfe){ 
        JOptionPane.showMessageDialog(this, "Numerical entry expected. Please try again");

另外，请注意，您应始终在showXXXDialog中传递父组件，以使对话框成为模块（即阻止访问）此组件的框架。你读过javadoc of JOptionPane了吗？您是否阅读过tutorial about dialogs？

在GUI中处理异常的问题

1 个答案: