更正 Book 类以获取 getBooksByAuthor 方法的输出

Question

我正在尝试获取 getBooksByAuthor 方法的输出，但它没有返回任何其他方法正在工作

我需要一个无需更改 getBooksByAuthor 方法且仅更改 Book 类的解决方案。

import java.util.*;

class Book  {
    // this class can modified if necessary, including the class definition
    private String title;
    private String author;
    private double price;

 public Book(String title, String author, double price) {
    this.title = title;
    this.author = author;
    this.price = price;
 }

 public String getTitle() {
    return title;
 }

 public String getAuthor() {
    return author;
 }

 public double getPrice() {
   return price;
 }

}

class Bookstore  {
  List<Book> books = new ArrayList<Book>();

  public Bookstore(List<Book> books) {
  this.books = books;
}

  public List<Book> getBooksSortedByPrice(int order) {
     if(order==0){
         for(double outer=0; outer < books.size()-1; outer++)
         {
          for(double inner=outer; inner < books.size(); inner++)
          {
           if(Integer.toString((int) books.get((int) outer).getPrice()).compareTo(Integer.toString((int)books.get((int) inner).getPrice()))>0)  {  
              Book temp = books.get((int) outer);
              books.set((int) outer, books.get((int) inner));
              books.set((int) inner, temp);
          }
        }
 }}        

        if(order==1){
         for(double outer=0; outer < books.size()-1; outer++)
     {
     for(double inner=outer; inner < books.size(); inner++)
    {
       if(Integer.toString((int) books.get((int) outer).getPrice()).compareTo(Integer.toString((int) books.get((int) inner).getPrice()))<0)  {  
      Book temp = books.get((int) outer);
      books.set((int) outer, books.get((int) inner));
      books.set((int) inner, temp);
   }

}
 }}        




   return books;
   }

 public List<Book> getBooksSortedByTitle(int order) {

     if(order==0){
         for(int outer=0; outer < books.size()-1; outer++)
         {
     for(int inner=outer; inner < books.size(); inner++)
        {
        if(books.get(outer).getTitle().compareTo(books.get(inner).getTitle())>0)  {  
         Book temp = books.get(outer);
         books.set(outer, books.get(inner));
         books.set(inner, temp);
       }

    }
 }}
    if(order==1){
     System.out.println("isu = ");
    for(int outer=0; outer < books.size()-1; outer++)
  {
    for(int inner=outer; inner < books.size(); inner++)
    {
   if(books.get(outer).getTitle().compareTo(books.get(inner).getTitle())<0)  {  
      Book temp = books.get(outer);
      books.set(outer, books.get(inner));
      books.set(inner, temp);
   }

}
 }}        

return books;
}

 public List<Book> getBooksByAuthor(String author) {
// this method returns the list of books for a given author
// do not make any changes to this method
// change the Book class to make sure this method will work correctly
List<Book> result = new ArrayList<Book>();
Book helperBook = new Book("Dummy", author, 0.0);
for (Book b : books) {
    if (b.equals(helperBook)) {
        result.add(b);
    }
}
return result;
}
 }

 public class Q2 {

/**
 * @param args the command line arguments
*/
public static void main(String[] args) {



    List<Book> book = new ArrayList<Book>();

   book.add(new Book("Java Programming", "Joyce Farrell", 881.0));
   book.add( new Book("Team Of Rivals", "Dorris Kearns Goodwin", 994));
   book.add (new Book("1776", "Daivd McCullough", 400));
   book.add (new Book("No Ordinary Time", "Dorris Kearns Goodwin", 768));
   book.add( new Book("Steve Jobs", "Walter Isaacson", 656));

  book.add( new Book("Dummy","Walter",0.0));
  book.add( new Book("Dummy","Walter",0.0)); 
  Bookstore df=new Bookstore(book);


  List<Book> booksSorted = df.getBooksByAuthor("Walter");
  for (Book number : booksSorted) {




  System.out.println( number.getPrice()+"--as--"+number.getTitle()+"----"+number.getAuthor());



  }



}

}

Answer 1

您应该通过实现 IComparable 将实体 Book 添加为 Comparable。

class Book implements IComparable {

您还应该指定要比较的内容。 因此，将此方法添加到您的 Book 类中。

public int compareTo(object obj) {
    Book objBook = (Book)obj;
    return this.author.equals(objBook.author) ? 0 : -1;
}

这不是 compareTo 类的一个很好的实现，但由于你老师的奇怪要求，它就足够了。

Answer 2

您需要为您的图书类实现/覆盖 equals 和 hashCode 方法以便进行比较

if (b.equals(helperBook)) {
    result.add(b);
}

返回匹配的书籍。

像这样覆盖等于

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    Book book = (Book) o;

    if (Double.compare(book.price, price) != 0) return false;
    if (!author.equals(book.author)) return false;
    if (!title.equals(book.title)) return false;

    return true;
}

您可能需要也可能不需要覆盖哈希码

@Override
public int hashCode() {
    int result;
    long temp;
    result = title.hashCode();
    result = 31 * result + author.hashCode();
    temp = Double.doubleToLongBits(price);
    result = 31 * result + (int) (temp ^ (temp >>> 32));
    return result;
}

this link 解释了每个 java 对象上的 equals、hashCode 和其他默认方法的详细信息。

Answer 3

你需要在Book类中添加equals方法。

如果两个作者相同，它将返回 true。