Java GUIは試行時にエラーを返さない

Question

以下のコードに関しては、BOOKGUIクラスをBOOKSHELFクラスにアクセスさせてメソッドから値を返そうとしています。 BOOKGUIクラス

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

if (e.getActionCommand().equals("Size of BookShelf")) 
      return books.size(); 

BOOKGUI CLASS

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 

{ 

    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 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(int 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("Author"); 
     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"); 
     book.setTitle(title); 
     book.setAuthor(author); 
     book.setPublisher(publisher); 

      bookShelf.addBook(book); 

     // set up each individual title, author, etc. use joptionpane and mutators? 
     //exception handling... 
     // add the book to the bookShelf 

     String message = "The title of the book is :" + title + 
     "the Author of the Book is : " + author + " and it's published by " + publisher; 
     //TAKE A LOOK AT THIS //JOptionPane.showMessageDialog(
       //null, " The sum is " + sum, "Results", 
       //JOptionPane.PLAIN_MESSAGE); 

     //System.exit(0); 
     JOptionPane.showMessageDialog(null, message, "Book Details", JOptionPane.PLAIN_MESSAGE); 

     //Container content = getContentPane(); 
     if (e.getActionCommand().equals("Size of BookShelf")) 
      return books.size(); 

      //return sizeofBookshelf(); 
     //String message = "Number of books in shelf "+books.sizeOfBookshelf(); 
     //JOptionPane.showMessageDialog(null, message, "Book Shelf", JOptionPane.PLAIN_MESSAGE); 

    //sizeOfBookshelf = JOptionPane.showInputDialog("Size"); 
    //sizeOfBookshelf = Integer.valueOf(JOptionPane.showInputDialog(null, "Enter size of bookshelf")); 

     //label2 = new JButton("Get Book Information"); 
     //content.add(label2); 

     //JButton label3 = new JButton("Show Total Cost of Books"); 
     //content.add(label3); 

    } 
} 

BOOKSHELF CLASS 0123で、次のようなものを使用して

BOOKSHELF CLASS

public int sizeOfBookshelf() 
{ 
    return books.size(); 
} 

import java.util.ArrayList; 

/** 
    * This class holds an ArrayList of Book. There are methods for adding Book objects to the ArrayList, 
    * calculating the total cost of all books in the ArrayList, determining how many Book objects are 
    * in the ArrayList and determining the highest price paid for any one Book. 
    * 
    * @version 1.0 
    */ 

public class BookShelf 
{ 
    //create an ArrayList of Book. 
    public ArrayList<Book> books; 

    public BookShelf() 
    {  
     books = new ArrayList<Book>(); 
    } 

    /** 
    * This method adds a Book object to the ArrayList 
    * 
    * @param theBook The book object that will be added to the ArrayList 
    * 
    */ 
    public void addBook(Book theBook) 
    { 
     books.add(theBook); 
    } 

    /** 
    * This method returns the size of the ArrayList, that is, the number of books 
    * that have been added to the ArrayList 
    * 
    * @return The size of the ArrayList 
    */ 
    public int sizeOfBookshelf() 
    { 
     return books.size(); 
    } 

    /** 
    * This method calculates the cost of the book shelf, that is, it totals the 
    * cost of all the books in the ArrayList and returns it. 
    * 
    * @return The cost of the book shelf 
    */ 
    public double costOfBookshelf(){ 

     double total = 0; 

     for(Book book : books) { 
      total = total + book.getCost(); 
     } 
     return total; 
    } 


    //create a method called highestPricePAid that will return the cost of the most expensive book in the ArrayList 

    /** 
    * This method finds the price of the most expensive book in the ArrayList and returns it. 
    * 
    * @return The cost of the most expensive book on the book shelf 
    */ 
    public double highestPricePaid(){ 

     double highestPrice = 0; 

     for(Book book : books) { 

      if((highestPrice == 0) || (highestPrice < book.getCost())) { 
       highestPrice = book.getCost(); } 
     }   
     return highestPrice; 
    }    
} 

ただし、Eclipseでエラーが発生しています。 完全に間違っているのですか？


ご協力いただければ幸いです。おかげ

Answer 1

あなたはbookShelfオブジェクトにsizeOfBookshelfメソッドを呼び出したい場合は、構文は

bookShelf.sizeOfBookshelf() 

ある、ない

books.size() 

また、actionPerformedの戻り型はvoidです。 voidメソッドからint値を返すことはできません。

if (e.getActionCommand().equals("Size of BookShelf")) { 
    int sizeOfBookShelf = bookShelf.sizeOfBookshelf(); 
    String message = "The book shelf has " + sizeOfBookShelf + " book(s)"; 
    JOptionPane.showMessageDialog(this, message); 
} 

Answer 2

は、これは宿題のように見えるので、私はあなたにヒントを与えている:)

をあなたのJButtonのアクションのコマンドを設定するための最初の必要性

e.getActionCommand() 

ような何かを行うには：

を

buttonX.setActionCommand("do something"); 

詳細については、ActionEventおよびsetActionCommand()を参照してください。