Java isLong（）方法不工作

我一直在试图弄明白为什么这段代码已经好几个小时没用了，而且我对ArrayList方法还是相当陌生的。基本上，

isLong

方法不起作用，我不确定原因。编译器说“找不到方法-方法isLong”

错误：

import java.util.Scanner;
import java.io.*;
import java.util.ArrayList;
public class BookCollection
{
    private ArrayList<Book> bookList;
    public BookCollection() throws Exception
    {
        bookList = new ArrayList<Book>();
        String firstLine, isbnI, authorI, areaI;
        int lengthI;
        Book book;
        Scanner FILE, fileScan;
        fileScan = new Scanner(new File("Books.txt"));
            while (fileScan.hasNext())
            {
              firstLine = fileScan.nextLine();
              FILE = new Scanner(firstLine);
              isbnI = FILE.next();
              authorI = FILE.next();
              areaI = FILE.next();
              lengthI = FILE.nextInt();
              book = new Book(isbnI, authorI, areaI, lengthI);
              bookList.add(book);
            }
    }
    public void displayLongBooks()
    {
      System.out.println("LONG BOOKS\n\n");
      for(int i = 0; i < bookList.size(); i++)
      {
        if (bookList.get(i).isLong())
        {
          return System.out.println(bookList.get(i)+"\n");
        }
      }
    }
    void displayBooksFromAuthor(String Author)
    {
      for (int i = 0; i < bookList.size(); i++)
      {
        if (bookList.get(i).author.equals(Author))
          System.out.println(bookList.get(i));
      }
    }
    void displayBooksFromArea(String Area)
    {
      for (int i = 0; i < bookList.size(); i++)
      {
        if (bookList.get(i).area.equals(Area))
          System.out.println(bookList.get(i));
      }
    }
    Book longestBook()
    {
        int maxId = 0;
        int currMax = 0;
        for(int i=0; i < bookList.size(); i++)
        {
          Book currBook = bookList.get(i);
          if(currBook.getLength() > currMax)
          {
            currMax = currBook.getLength();
            maxIdx = i;
          }
        }
        return bookList.get(maxIdx);
    }

}
`

主要方法：

`
import java.util.Scanner;
public class TestBookCollection
{
  public static void main(String[] args) throws Exception
  {
    Scanner scan = new Scanner(System.in);
    BookCollection testBooks = new BookCollection();

    System.out.println(testBooks);
    System.out.println();
    testBooks.displayLongBooks();
    System.out.println("\nChoose an author: ");
    String author = scan.next();
    testBooks.displayBooksFromAuthor(author);
    System.out.println("\nChoose an area: ");
    String area = scan.next();
    testBooks.displayBooksFromArea(area);
  }
}
`

---

您将方法声明为

islong

而不是

islong

您的方法称为islong。。。这里没有L。Java标识符区分大小写：您调用

isLong

，但声明了

isLong

。还要注意：使用布尔表达式选择true/false是完全多余的-直接使用表达式：“返回长度>=400；”哇。。非常感谢你，我不敢相信我竟然没有意识到。。。

`
import java.util.Scanner;
public class TestBookCollection
{
  public static void main(String[] args) throws Exception
  {
    Scanner scan = new Scanner(System.in);
    BookCollection testBooks = new BookCollection();

    System.out.println(testBooks);
    System.out.println();
    testBooks.displayLongBooks();
    System.out.println("\nChoose an author: ");
    String author = scan.next();
    testBooks.displayBooksFromAuthor(author);
    System.out.println("\nChoose an area: ");
    String area = scan.next();
    testBooks.displayBooksFromArea(area);
  }
}
`