如何从文件填充对象数组？解决BufferedReader实现时的数组越界问题

Let's break down the issues in your code one by one and fix them, plus offer some alternative approaches to make this more robust.

核心问题导致数组越界 #

Your ArrayIndexOutOfBoundsException stems from two critical mistakes:

1. Index reset inside the loop: You initialize int i = 0; inside the while loop, so every time you read a line, you're overwriting arbook[0] instead of moving to the next index. Worse, when you hit the final comment line ((( Name,Author,Released,numCopies,properAge,science <boolean> ))), splitting this line with " " gives an array with only 1 element—trying to access ar[1] here throws the exception.
2. Unfiltered input: Your code attempts to process every line in the file, including the non-data comment line that doesn't follow the 5-field format.

其他需要修正的代码问题 #

Beyond the exception, there are a few other issues violating Java conventions or best practices:

• Case sensitivity: Java is case-sensitive. You declared your array as static book arbook[], but your class is named Book (capital B)—this will cause a compilation error.
• Resource leak: You don't close your BufferedReader, which can lead to resource leaks. Use try-with-resources to handle this automatically.
• Hardcoded array size: You set arbook to size 14, but if your file ever has more or fewer valid lines, this will cause new errors.
• CamelCase inconsistencies: Your properAge getter is named getProperage (missing capital A), which breaks Java naming conventions.

修正后的完整代码 #

Here's the fixed version that addresses all these issues:

import java.io.*;
import java.util.logging.Level;
import java.util.logging.Logger;

public class BooksReader {
    // Fix class name case, use a static index to track position
    static Book arbook[] = new Book[14];
    static int currentIndex = 0;

    public static void array_filler() throws FileNotFoundException {
        // Try-with-resources auto-closes BufferedReader
        try (BufferedReader br = new BufferedReader(new FileReader("MyPath"))) {
            String line;
            while ((line = br.readLine()) != null) {
                // Skip empty lines and the final comment line
                if (line.isBlank() || line.startsWith("((")) {
                    continue;
                }
                String[] ar = line.split(" ");
                // Validate line has exactly 5 fields before processing
                if (ar.length != 5) {
                    System.out.println("Skipping invalid line: " + line);
                    continue;
                }
                try {
                    // Assign to current index and increment
                    arbook[currentIndex] = new Book(
                            ar[0],
                            ar[1],
                            Integer.parseInt(ar[2]),
                            Integer.parseInt(ar[3]),
                            Integer.parseInt(ar[4])
                    );
                    currentIndex++;
                } catch (NumberFormatException e) {
                    System.out.println("Invalid number format in line: " + line);
                }
            }
        } catch (IOException ex) {
            Logger.getLogger(BooksReader.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public static void main(String[] args) throws FileNotFoundException {
        BooksReader.array_filler();
    }
}

// Ensure class name is consistent (capital B)
class Book {
    private String bookName;
    private String bookAuthor;
    private String serialNumber; // Renamed to camelCase
    private int numCopies;
    private int properAge;
    private int bookReleaseDate;

    public Book(String bookName, String bookAuthor, int bookReleaseDate, int numCopies, int properAge) {
        this.bookName = bookName;
        this.bookAuthor = bookAuthor;
        this.bookReleaseDate = bookReleaseDate;
        this.numCopies = numCopies;
        this.properAge = properAge;
    }

    // Fixed getter name for properAge
    public String getBookName() {
        return bookName;
    }

    public int getNumCopies() {
        return numCopies;
    }

    public int getProperAge() {
        return properAge;
    }

    public void setBookName(String bookName) {
        this.bookName = bookName;
    }

    public void setBookAuthor(String bookAuthor) {
        this.bookAuthor = bookAuthor;
    }

    public void setReleaseDate(int bookReleaseDate) {
        this.bookReleaseDate = bookReleaseDate;
    }

    public void setNumCopies(int numCopies) {
        this.numCopies = numCopies;
    }

    public void setProperAge(int properAge) {
        this.properAge = properAge;
    }

    public void setSerialNumber(String serialNumber) {
        this.serialNumber = serialNumber;
    }

    public boolean checkAge(int ageOfUser) {
        return ageOfUser >= properAge;
    }

    public int addNumCopies() {
        return ++this.numCopies;
    }

    public int decNumCopies() {
        return --this.numCopies;
    }
}

更灵活的替代实现思路 #

For a more maintainable solution, consider these alternatives:

1. Use ArrayList<Book> instead of a fixed array: This eliminates hardcoded size limits and handles variable numbers of entries automatically:

   static List<Book> books = new ArrayList<>();
   // Replace array assignment with:
   books.add(new Book(...));
   

2. Use Scanner for simpler token parsing: Scanner is built for reading tokenized input and can avoid manual string splitting:

   try (Scanner scanner = new Scanner(new File("MyPath"))) {
       while (scanner.hasNext()) {
           String bookName = scanner.next();
           String author = scanner.next();
           int releaseDate = scanner.nextInt();
           int numCopies = scanner.nextInt();
           int properAge = scanner.nextInt();
           books.add(new Book(bookName, author, releaseDate, numCopies, properAge));
           // Skip the final comment line
           if (scanner.hasNextLine() && scanner.nextLine().startsWith("((")) {
               break;
           }
       }
   }
   

3. Use a CSV library: If your file might later include spaces in titles/author names, libraries like OpenCSV can handle proper parsing without manual split logic.

内容的提问来源于stack exchange，提问作者Yusuf Abdelfattah