我正在开发一个简单的程序，它读取包含书名和相关参考号的文本文件。应将每组信息转换为Book对象，以便以后对其进行排序。但是，在当前代码中，每当应创建新书时，它都会重新使用原始书。我在Book类中添加了一个计数器来跟踪Book对象的数量。
程序应使用书名和相关参考号创建一个新的Book对象。 为了解决此问题，我会更改/添加哪些内容？
主要类
private static ArrayList<Book> books = new ArrayList();
public static void main(String[] args) {
String path = "src//booklist.txt";
boolean endOfFile = false;
// try/catch for reading the file
try {
FileReader fr = new FileReader(path);
BufferedReader br = new BufferedReader(fr);
while (!endOfFile) {
String line = br.readLine();
if (line == null) {
endOfFile = true;
} else {
books.add(new Book(null, 0));
books.get(books.size() - 1).setRefNum(Integer.parseInt(line));
String bookTitle = br.readLine();
books.get(books.size() - 1).setTitle(bookTitle);
}
System.out.println(books.get(books.size() - 1).toString());
}
// Closing reader and displaying results
br.close();
} catch (IOException e) {
System.out.println(e.toString());
}
}
}
图书类
private String bookTitle;
private int refNum;
private int numBooks;
public Book(String title, int referenceNumber) {
this.bookTitle = title;
this.refNum = referenceNumber;
this.numBooks++;
}
public String getTitle() {
return this.bookTitle;
}
public void setTitle(String title) {
this.bookTitle = title;
}
public int getRefNum() {
return this.refNum;
}
public void setRefNum(int referenceNumber) {
this.refNum = referenceNumber;
}
public int getNumBooks() {
return this.numBooks;
}
public String toString() {
String message = "Book Title: " + this.bookTitle
+ "\nReference #: " + this.refNum
+ "\nBook #: " + this.numBooks
+ "\n";
return message;
}
文字广告（ booktitles.txt ）
1
The Adventures of Tom Sawyer
2
Huckleberry Finn
4
The Sword in the Stone
6
Stuart Little
10
Treasure Island
12
The Secret Garden
14
Alice's Adventures in Wonderland
20
Twenty Thousand Leagues Under the Sea
24
Peter Pan
26
Charlotte's Web
31
A Little Princess
32
Little Women
33
Black Beauty
35
The Merry Adventures of Robin Hood
40
Robinson Crusoe
46
Anne of Green Gables
50
Little House in the Big Woods
52
Swiss Family Robinson
54
The Lion, the Witch and the Wardrobe
56
Heidi
66
A Winkle in Time
100
Mary Poppins
当前输出
Book Title: The Adventures of Tom Sawyer
Reference #: 1
Book #: 1
Book Title: Huckleberry Finn
Reference #: 2
Book #: 1
Book Title: The Sword in the Stone
Reference #: 4
Book #: 1
Book Title: Stuart Little
Reference #: 6
Book #: 1
Book Title: Treasure Island
Reference #: 10
Book #: 1
Book Title: The Secret Garden
Reference #: 12
Book #: 1
Book Title: Alice's Adventures in Wonderland
Reference #: 14
Book #: 1
Book Title: Twenty Thousand Leagues Under the Sea
Reference #: 20
Book #: 1
Book Title: Peter Pan
Reference #: 24
Book #: 1
Book Title: Charlotte's Web
Reference #: 26
Book #: 1
Book Title: A Little Princess
Reference #: 31
Book #: 1
Book Title: Little Women
Reference #: 32
Book #: 1
Book Title: Black Beauty
Reference #: 33
Book #: 1
Book Title: The Merry Adventures of Robin Hood
Reference #: 35
Book #: 1
Book Title: Robinson Crusoe
Reference #: 40
Book #: 1
Book Title: Anne of Green Gables
Reference #: 46
Book #: 1
Book Title: Little House in the Big Woods
Reference #: 50
Book #: 1
Book Title: Swiss Family Robinson
Reference #: 52
Book #: 1
Book Title: The Lion, the Witch and the Wardrobe
Reference #: 54
Book #: 1
Book Title: Heidi
Reference #: 56
Book #: 1
Book Title: A Winkle in Time
Reference #: 66
Book #: 1
Book Title: Mary Poppins
Reference #: 100
Book #: 1
所需输出
Book Title: The Adventures of Tom Sawyer
Reference #: 1
Book #: 1
Book Title: Huckleberry Finn
Reference #: 2
Book #: 2
Book Title: The Sword in the Stone
Reference #: 4
Book #: 3
Book Title: Stuart Little
Reference #: 6
Book #: 4
Book Title: Treasure Island
Reference #: 10
Book #: 5
Book Title: The Secret Garden
Reference #: 12
Book #: 6
Book Title: Alice's Adventures in Wonderland
Reference #: 14
Book #: 7
Book Title: Twenty Thousand Leagues Under the Sea
Reference #: 20
Book #: 8
Book Title: Peter Pan
Reference #: 24
Book #: 9
Book Title: Charlotte's Web
Reference #: 26
Book #: 10
Book Title: A Little Princess
Reference #: 31
Book #: 11
Book Title: Little Women
Reference #: 32
Book #: 12
Book Title: Black Beauty
Reference #: 33
Book #: 13
Book Title: The Merry Adventures of Robin Hood
Reference #: 35
Book #: 14
Book Title: Robinson Crusoe
Reference #: 40
Book #: 15
Book Title: Anne of Green Gables
Reference #: 46
Book #: 16
Book Title: Little House in the Big Woods
Reference #: 50
Book #: 17
Book Title: Swiss Family Robinson
Reference #: 52
Book #: 18
Book Title: The Lion, the Witch and the Wardrobe
Reference #: 54
Book #: 19
Book Title: Heidi
Reference #: 56
Book #: 20
Book Title: A Winkle in Time
Reference #: 66
Book #: 21
Book Title: Mary Poppins
Reference #: 100
Book #: 22
答案 0 :(得分：2)
我认为你误解了代码
books.add(new Book(null, 0));
books.get(books.size() - 1).setRefNum(Integer.parseInt(line));
String bookTitle = br.readLine();
books.get(books.size() - 1).setTitle(bookTitle);
每次都会创建一个新的Book。然而，这是低效的。考虑
Book b = new Book(null,0);
books.add(b);
b.setRefNum(Integer.parseInt(line));
String bookTitle = br.readLine();
b.setTitle(bookTitle);
变量b是循环的本地变量。更好的是，使用构造函数
String bookTitle = br.readLine();
Book b = new Book(bookTitle,Integer.parseInt(line));
books.add(b);
关于澄清的问题：
numBooks是一个实例变量，因此每本书都有一个副本。您需要的是使用books.size()来检索列表中的条目数。从numBooks课程中删除Book，没有必要。
答案 1 :(得分：0)
在构造函数中使用正确的值，以便不需要添加dummy本书，随后got以便更新
String bookTitle = br.readLine();
books.add(new Book(bookTitle, Integer.parseInt(line)));
答案 2 :(得分：0)
替换
行books.add(new Book(null, 0));
books.get(books.size() -1).setRefNum(Integer.parseInt(line));
String bookTitle = br.readLine();
books.get(books.size() - 1).setTitle(bookTitle);
通过
String bookTitle = br.readLine();
books.add(new Book(bookTitle,Integer.parseInt(line)));
你的问题出在带有numBooks的Book类中。你不需要这个。您可以使用arrayList书籍及其索引作为输出。
答案 3 :(得分：0)
添加到Book类的计数器不是静态的。因此，对于Book对象的每个新实例，它都是唯一的。所以它永远是一个。
private int numBooks;
public Book(String title, int referenceNumber) {
this.bookTitle = title;
this.refNum = referenceNumber;
this.numBooks++;
}
你没有看到从ArrayList书籍对象中添加多本书吗？
System.out.println(books.get(books.size() - 1).toString());
答案 4 :(得分：0)
根据您当前的输出，标题正在变化，但书籍＃不会改变。
让numBooks成为静态。 Static变量与类链接而不是类的实例，因此相同的变量将在作为同一个类的实例的所有对象之间共享。