比较器双倍不起作用 [英] Comparator double does not work
本文介绍了比较器双倍不起作用的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我开发了一个程序，该程序创建一个Book对象数组，并根据用户输入对它们进行排序。排序选项为author-title-pages-price，除了价格排序外，其他所有选项均可用。
请帮助我找出为什么我不能使用比较器对双打进行排序...
我的SchoolTextBook类：
I have developed a program that creates an array of Book Objects and sorts them based on user input. The sorting options are author-title-pages-price, and all work but the price sort. Please help me find why I cannot sort doubles using Comparator... My SchoolTextBook Class:
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> BookAuthorComparator
= new Comparator<SchoolTextBook>() {
public int compare(SchoolTextBook book1, SchoolTextBook book2) {
String bookName1 = book1.getAuthor().toUpperCase();
String bookName2 = book2.getAuthor().toUpperCase();
//ascending order
return bookName1.compareTo(bookName2);
}
};
public static Comparator<SchoolTextBook> BookTitleComparator
= new Comparator<SchoolTextBook>() {
public int compare(SchoolTextBook book1, SchoolTextBook book2) {
String bookName1 = book1.getTitle().toUpperCase();
String bookName2 = book2.getTitle().toUpperCase();
//ascending order
return bookName1.compareTo(bookName2);
}
};
public static Comparator<SchoolTextBook> BookPagesComparator
= new Comparator<SchoolTextBook>() {
public int compare(SchoolTextBook book1, SchoolTextBook book2) {
int bookName1 = book1.getPageCount();
int bookName2 = book2.getPageCount();
//ascending order
return bookName1 - bookName2;
}
};
public static Comparator<SchoolTextBook> BookPriceComparator
= new Comparator<SchoolTextBook>() {
public int compare(SchoolTextBook book1, SchoolTextBook book2) {
double bookName1 = book1.getPrice();
double bookName2 = book2.getPrice();
//ascending order
return (int) (bookName1 - bookName2);
}
};
}
以及排序程序：
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();
}
}
推荐答案
使用您现有的解决方案，您会将差异投射到 int 上，这在所有情况下都不起作用，例如 2.5 和 2.6 将解析为（int）（2.6- 2.5） = 0 意味着它们都是相同的以避免它
With your existing solution you are casting the difference to int which will not work in all case, for example 2.5 and 2.6 will resolve to (int)(2.6- 2.5) = 0 that means both of them are same to avoid it
使用 Double.compare（double，double） 代替
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);
}
};
这篇关于比较器双倍不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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