Question

我创建了一个从文件读取的代码，每一行都是一本不同的书，并且每一行都包含一个标题和一个价格。图书文件为：

    The Hobbit,$15.00
    Purple Cow,$10.00
    Death by Black Hole,$35.00

该方法有效。但我尝试创建一种工作方式如下：输入预算：15，然后将所有交易的价格降低到15美元以下。我已经完成了searchForPrice方法的一部分，但实际上并没有解决。我该怎么办？谢谢。

import java.util.*;
import java.io.*;
import javax.swing.*;
public class BookStore {
    private ArrayList<Book> library;
    String Book;

    public BookStore() throws FileNotFoundException {
        library = readBooks("books1.txt");
    }
    public ArrayList<Book> readBooks(String path) {
        ArrayList<Book> books = new ArrayList<Book>();

        try{
            BufferedReader br = new BufferedReader(new FileReader(path));
            String line;
            while ((line = br.readLine()) != null) {
                String[] arr = line.split(",");
                String title = arr[0];
                double price = Double.parseDouble(arr[1].trim().replace("$",""));//in case has a $
                books.add(new Book(title,price));

            }
            br.close();
        }
        catch (Exception e){
            e.printStackTrace();
        }
        return books;
    }

    public String toString() {
        String result = "";
        for (Book tempBook : library) {
            result += tempBook.toString() + "\n";
        }
        return result;
    }

    public ArrayList<Book> searchForTitle(String searchString) {
        ArrayList<Book> searchResult = new ArrayList<Book>();
        for (Book currentBook : library) {
            if ((currentBook.getTitle()).indexOf(searchString) != -1)
                searchResult.add(currentBook);
        }
        searchResult.trimToSize();
        return searchResult;
    }

    //get lowest price book
    public Book lowestPrice() {
        Book lowestPrice = library.get(0);
        for (Book book : library) {
            if (book.getPrice() < lowestPrice.getPrice()) {
                lowestPrice = book;
            }
        }
        return lowestPrice;
    }

    //bookslessthanthenumbertheyenter
    public ArrayList<Book> searchForPrice(double searchdouble) {
        ArrayList<Book> searchPrice = new ArrayList<Book>();
        for (Book currentBook : library) {
            if ((currentBook.getPrice()).Double.parseDouble.indexOf(searchdouble) != -1)
                searchPrice.add(currentBook);
        }
        searchPrice.trimToSize();
        return searchPrice;
    }
}

Answer 1

此循环甚至可以编译：

for (Book currentBook : library) {
    if ((currentBook.getPrice()).Double.parseDouble.indexOf(searchdouble) != -1)
        searchPrice.add(currentBook);
}

在Book类中，您将价格存储为double，因此无需转换，只需将每本书的价格与searchdouble进行比较：

for (Book currentBook : library) {
    if (currentBook.getPrice() < searchdouble)
        searchPrice.add(currentBook);
}

还有您为什么需要：

searchPrice.trimToSize();

因为您没有声明任何初始容量？

Answer 2

在Java中，比较Doubles的最好方法是使用Double类 compare 提供的功能。

所以代码看起来像这样。

if (Double.compare(currentBook.getPrice(), searchdouble) <= 0)

如果函数比较相等，则它们将返回0；如果第一个较低，则返回-1；如果较高，则返回1。

ArrayList从文件中读取行并将其分配

2 个答案: