我创建了一个书单的 Java 类。
public class bookList {
public String title, author, genre;
public bookList (String beginTitle, String beginAuthor, String beginGenre)
{
title = beginTitle;
author = beginAuthor;
genre = beginGenre;
}
public String getTitle(){return title;}
public String getAuthor(){return author;}
public String getGenre(){ return genre;}
public void setTitle(String titleUpdate){title = titleUpdate;}
public void setAuthor(String authorUpdate){author = authorUpdate;}
public void setPubDate(String genreUpdate){genre = genreUpdate;}
@Override
public String toString() {
return "title: " + title + '\t'+
"author: " + author + '\t'+
"genre: " + genre +
"\n";
}
}
然后我创建了一个驱动程序类，将书籍添加到 toRead ArrayList 中。
import java.util.*;
public class Main {
public static void main(String[] args) {
int userResponse = 1;
String title, author, genre;
String userInput;
Scanner scan = new Scanner(System.in);
bookList newBook = new bookList(" ", " ", " ");
ArrayList<bookList> toRead = new ArrayList<>();
bookList example1 = new bookList("Mesopotamia", "Gwendolyn Leick", "history");
bookList example2 = new bookList("A Week to be Wicked", "Tessa Dare", "romance");
bookList example3 = new bookList("Say Yes to the Marquess", "Tessa Dare", "romance");
bookList example4 = new bookList("Istanbul", "Thomas F. Madden", "history");
bookList example5 = new bookList("Circe", "Madeline Miller", "fiction");
bookList example6 = new bookList("The Song of Achilles", "Madeline Miller", "fiction");
bookList example7 = new bookList("A Lady by Midnight", "Tessa Dare", "romance");
bookList example8 = new bookList("When a Scot Ties the Knot", "Tessa Dare", "romance");
bookList example9 = new bookList("Worlds of Medieval Europe", "Clifford Backman", "history");
bookList example10 = new bookList("The Sumerians", "Samuel Noah Kramer", "history");
Collections.addAll(toRead, example1, example2, example3, example4, example5, example6, example7, example8, example9, example10);
System.out.println("Welcome to your to read list!");
System.out.println("To see your reading list, enter 1,");
System.out.println("To sort your reading list by title, type 2");
userResponse = scan.nextInt();
if (userResponse == 1) {
System.out.println(toRead);
}
if (userResponse == 2) {
Collections.sort(toRead);
}
}
Collections.sort(toRead);用红色下划线表示“不存在类型变量 T 的实例，因此 bookList 符合 Comparable”
我尝试过谷歌和其他问题，但没有帮助。如有任何帮助，我们将不胜感激。谢谢！
（在有人问之前，是的，这是家庭作业。我们应该设计和创建一个程序。我们没有在课堂上讨论对数组列表进行排序）。
我认为类
bookListBooktoStringequalshashCodeComparable请注意，以下代码使用 lambda 表达式（和方法引用）。
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
public record Book(String title, String author, String genre) {
public static void main(String[] args) {
Comparator<Book> bookTitleComparator = (b1, b2) -> b1.title().compareTo(b2.title);
List<Book> bookList = new ArrayList<>();
bookList.add(new Book("Mesopotamia", "Gwendolyn Leick", "history"));
bookList.add(new Book("A Week to be Wicked", "Tessa Dare", "romance"));
bookList.add(new Book("Say Yes to the Marquess", "Tessa Dare", "romance"));
bookList.add(new Book("Istanbul", "Thomas F. Madden", "history"));
bookList.add(new Book("Circe", "Madeline Miller", "fiction"));
bookList.add(new Book("The Song of Achilles", "Madeline Miller", "fiction"));
bookList.add(new Book("A Lady by Midnight", "Tessa Dare", "romance"));
bookList.add(new Book("When a Scot Ties the Knot", "Tessa Dare", "romance"));
bookList.add(new Book("Worlds of Medieval Europe", "Clifford Backman", "history"));
bookList.add(new Book("The Sumerians", "Samuel Noah Kramer", "history"));
bookList.stream()
.sorted(bookTitleComparator)
.forEach(System.out::println);
}
}
运行上面代码时的输出：
Book[title=A Lady by Midnight, author=Tessa Dare, genre=romance]
Book[title=A Week to be Wicked, author=Tessa Dare, genre=romance]
Book[title=Circe, author=Madeline Miller, genre=fiction]
Book[title=Istanbul, author=Thomas F. Madden, genre=history]
Book[title=Mesopotamia, author=Gwendolyn Leick, genre=history]
Book[title=Say Yes to the Marquess, author=Tessa Dare, genre=romance]
Book[title=The Song of Achilles, author=Madeline Miller, genre=fiction]
Book[title=The Sumerians, author=Samuel Noah Kramer, genre=history]
Book[title=When a Scot Ties the Knot, author=Tessa Dare, genre=romance]
Book[title=Worlds of Medieval Europe, author=Clifford Backman, genre=history]
由于 [Java] 记录实际上是一个类，因此您还可以重写任何方法，例如
toString正如评论中所指出的，您没有为您的程序提供一种对“bookList”进行排序的方法。它应该根据倾斜对其进行排序吗？作者？还有别的东西吗？ java 不会仅仅假设“bookList”的自然顺序是什么。
您必须告诉您的程序根据特定条件进行排序，例如标题、作者或类中的任何其他数据字段。
实现此目的的一种方法是让“bookList”类实现 Comparable 接口并重写compareTo() 方法
public class bookList implements Comparable<bookList>{
public String title, author, genre;
public bookList (String beginTitle, String beginAuthor, String beginGenre)
{
title = beginTitle;
author = beginAuthor;
genre = beginGenre;
}
public String getTitle() {
return title;
}
public String getAuthor() {
return author;
}
public String getGenre() {
return genre;
}
public void setTitle(String titleUpdate) {
title = titleUpdate;
}
public void setAuthor(String authorUpdate) {
author = authorUpdate;
}
public void setPubDate(String genreUpdate) {
genre = genreUpdate;
}
@Override
public String toString() {
return "title: " + title + '\t'+
"author: " + author + '\t'+
"genre: " + genre +
"\n";
}
@Override
public int compareTo(bookList other) {
//assuming you want to sort by tilte, change it as per your requirements
return this.title.compareTo(other.title);
}
}