Question

我开发了一个程序，可以创建一个Book Objects数组，并根据用户输入对它们进行排序。排序选项是作者 - 标题 - 页面 - 价格，所有工作，但价格排序。请帮我找到我的应用程序挂起的位置...（我点击按价格排序按钮，没有任何显示...）

我的SchoolTextBook课程：

import java.util.Comparator;


public class SchoolTextBook {

private String author;
private String title;
private int pageCount;
private String ISBN;
private double price;

public String getAuthor() {
    return author;
    }
public void setAuthor(String author) {
    this.author = author;
    }

public String getTitle() {
    return title;
    }
public void setTitle(String title) {
    this.title = title;
    }

public int getPageCount() {
    return pageCount;
}
public void setPageCount(int pageCount) {
    this.pageCount = pageCount;
}

public String getISBN() {
    return ISBN;
}
public void setISBN(String iSBN) {
    ISBN = iSBN;
}

public double getPrice() {
    return price;
}
public void setPrice(double price) {
    this.price = price;
}


public static Comparator<SchoolTextBook> BookPriceComparator 
                    = new Comparator<SchoolTextBook>() {

    public int compare(SchoolTextBook book1, SchoolTextBook book2) {

        double price1 = book1.getPrice();
        double price2 = book2.getPrice();
        //ascending order
        return Double.compare(price1, price2);

    }

};
}

我的SchoolTextBookSort课程：

import java.util.Arrays;
import java.util.*;

import javax.swing.*;

public class SchoolTextBookSort {

public static void main(String[] args) {
    // TODO Auto-generated method stub

    String[] choices = {"Author", "Title", "Page Count", "Price"};

    SchoolTextBook[] theBooks = new SchoolTextBook[5];

    theBooks[0] = new SchoolTextBook();
    theBooks[1] = new SchoolTextBook();
    theBooks[2] = new SchoolTextBook();
    theBooks[3] = new SchoolTextBook();
    theBooks[4] = new SchoolTextBook();

    theBooks[0].setAuthor("Ernest Hemingway");
    theBooks[1].setAuthor("Mark Twain");
    theBooks[2].setAuthor("William Shakespeare");
    theBooks[3].setAuthor("Stephen King");
    theBooks[4].setAuthor("William Faulkner");

    theBooks[0].setTitle("A Farewell to Arms");
    theBooks[1].setTitle("The Adventures of Huckleberry Finn");
    theBooks[2].setTitle("Hamlet");
    theBooks[3].setTitle("Salem's Lot");
    theBooks[4].setTitle("The Sound and the Fury");

    theBooks[0].setPageCount(332);
    theBooks[1].setPageCount(320);
    theBooks[2].setPageCount(196);
    theBooks[3].setPageCount(439);
    theBooks[4].setPageCount(326);

    theBooks[0].setISBN("0099910101");
    theBooks[1].setISBN("0142437174");
    theBooks[2].setISBN("0521618746");
    theBooks[3].setISBN("0450031063");
    theBooks[4].setISBN("0679732241");

    theBooks[0].setPrice(5.99);
    theBooks[1].setPrice(7.60);
    theBooks[2].setPrice(9.41);
    theBooks[3].setPrice(16.56);
    theBooks[4].setPrice(9.60); 


    int response = JOptionPane.showOptionDialog(
            null                                        // Center in window.
          , "Please select a method to sort the books." // Message
          , "Sort Text Books"                           // Title in titlebar
          , JOptionPane.YES_NO_OPTION                   // Option type
          , JOptionPane.PLAIN_MESSAGE                   // messageType
          , null                                        // Icon (none)
          , choices                                     // Button text as above.
          , null                                        // Default button's label
        );

    //... Use a switch statement to check which button was clicked.
    switch (response) {
    case 0: 
        Arrays.sort(theBooks, SchoolTextBook.BookAuthorComparator);
        break;
    case 1:
        Arrays.sort(theBooks, SchoolTextBook.BookTitleComparator);
        break;
    case 2:
        Arrays.sort(theBooks, SchoolTextBook.BookPagesComparator);
        break;
    case 3:
        Arrays.sort(theBooks, SchoolTextBook.BookPriceComparator);
    case -1:
        //... Both the quit button (3) and the close box(-1) handled here.
        System.exit(0);     // It would be better to exit loop, but...
    default:
        //... If we get here, something is wrong.  Defensive programming.
        JOptionPane.showMessageDialog(null, "Unexpected response " + response);
    }

    show(theBooks);


}

public static String show(SchoolTextBook[] theBooks) {
    StringBuilder sb = new StringBuilder(64);
    sb.append("<html><table><tr><td>Author</td><td>Title</td><td>ISBN</td><td>Pages</td><td>Price</td></tr>");
    sb.append("<tr>");
    sb.append("<td>").append(theBooks[0].getAuthor()).append("</td>");
    sb.append("<td>").append(theBooks[0].getTitle()).append("</td>");
    sb.append("<td>").append(theBooks[0].getISBN()).append("</td>");
    sb.append("<td>").append(theBooks[0].getPageCount()).append("</td>");
    sb.append("<td>").append("$" + theBooks[0].getPrice()).append("</td></tr>");
    sb.append("<tr>");
    sb.append("<td>").append(theBooks[1].getAuthor()).append("</td>");
    sb.append("<td>").append(theBooks[1].getTitle()).append("</td>");
    sb.append("<td>").append(theBooks[1].getISBN()).append("</td>");
    sb.append("<td>").append(theBooks[1].getPageCount()).append("</td>");
    sb.append("<td>").append("$" + theBooks[1].getPrice()).append("</td></tr>");
    sb.append("<tr>");
    sb.append("<td>").append(theBooks[2].getAuthor()).append("</td>");
    sb.append("<td>").append(theBooks[2].getTitle()).append("</td>");
    sb.append("<td>").append(theBooks[2].getISBN()).append("</td>");
    sb.append("<td>").append(theBooks[2].getPageCount()).append("</td>");
    sb.append("<td>").append("$" + theBooks[2].getPrice()).append("</td></tr>");
    sb.append("<tr>");
    sb.append("<td>").append(theBooks[3].getAuthor()).append("</td>");
    sb.append("<td>").append(theBooks[3].getTitle()).append("</td>");
    sb.append("<td>").append(theBooks[3].getISBN()).append("</td>");
    sb.append("<td>").append(theBooks[3].getPageCount()).append("</td>");
    sb.append("<td>").append("$" + theBooks[3].getPrice()).append("</td></tr>");
    sb.append("<tr>");
    sb.append("<td>").append(theBooks[4].getAuthor()).append("</td>");
    sb.append("<td>").append(theBooks[4].getTitle()).append("</td>");
    sb.append("<td>").append(theBooks[4].getISBN()).append("</td>");
    sb.append("<td>").append(theBooks[4].getPageCount()).append("</td>");
    sb.append("<td>").append("$" + theBooks[4].getPrice()).append("</td>");
    sb.append("</tr></table></html>");
    JOptionPane.showMessageDialog(null, sb);
    return sb.toString();
}

}

Answer 1

您需要在某些break条件中添加case语句：

switch (response) {
case 0: 
    Arrays.sort(theBooks, SchoolTextBook.BookAuthorComparator);
    break;
case 1:
    Arrays.sort(theBooks, SchoolTextBook.BookTitleComparator);
    break;
case 2:
    Arrays.sort(theBooks, SchoolTextBook.BookPagesComparator);
    break;
case 3:
    Arrays.sort(theBooks, SchoolTextBook.BookPriceComparator);
    break; // <---- Add this
case -1:
    //... Both the quit button (3) and the close box(-1) handled here.
    System.exit(0);     // It would be better to exit loop, but...
    break; // <---- Add this
default:
    //... If we get here, something is wrong.  Defensive programming.
    JOptionPane.showMessageDialog(null, "Unexpected response " + response);
    break; // <---- Add this
}

如果你没有break语句，程序会继续并评估所有低于它的情况，就好像它们是真的一样。换句话说，如果情况3为真，它会进行排序，那么它将继续进行情况-1中发生的事情，并且好像是真的，这会导致系统退出。

Answer 2

我发现问题在于此代码：

case -1:
    //... Both the quit button (3) and the close box(-1) handled here.
    System.exit(0);     // It would be better to exit loop, but...
default:
    //... If we get here, something is wrong.  Defensive programming.
    JOptionPane.showMessageDialog(null, "Unexpected response " + response);
}

不确定它究竟是什么，但这就是悬挂应用程序的原因。

使用比较器程序对双打进行排序

2 个答案: