[英]Java GUI error - Type mismatch: cannot convert from String to double
第100行的cost = JOptionPane.showInputDialog("Cost");
的附加代碼報告錯誤“類型不匹配:無法從字符串轉換為雙精度”-任何建議是什么原因引起的?
基本上,這是一個可訪問其他類'BookShelf'的類,並且此行是可訪問BookShelf類以返回costofBookshelf的actioncommand的一部分
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;
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("Title");
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");***
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;
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 " + costOfBookshelf + "Euro";
JOptionPane.showMessageDialog(this, message);
}
}
}
JOptionPane.showInputDialog返回一個字符串。 您不能將String值分配給double類型的變量。
您可以使用Double.parseDouble將String轉換為double。
cost
是雙showInputDialog
並且showInputDialog
返回一個字符串。 因此,您需要這樣做:
cost = Double.parseDouble(JOptionPane.showInputDialog("Cost"));
但是,如果這是用於生產代碼的,則可能應該添加一些驗證,以確保輸入的值實際上是數字。
cost = Double.parseDouble(JOptionPane.showInputDialog("Cost"));
使用double表示貨幣可能會給您帶來不好的結果 ,您應該考慮改用BigDecimal 。
您必須將輸入的字符串解析為雙精度型。
try {
code = Double.parseDouble(JOptionPane.showInputDialog("Cost"));
}
catch (NumberFormatException ex){
code = 0.0;
}
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