java - 如何使用Java中的扫描仪读取文本文件？

Question

这是我读取文本文件的代码。当我运行这段代码时，输​​出一直显示“找不到文件。”，这是 FileNotFoundException 的消息。我不确定这段代码有什么问题。

显然这是 java.lang 的一部分。对于整个 java 文件，它要求用户输入一些内容，并将使用输入作为名称创建一个文本文件。之后用户应该再次输入之前创建的文本文件的名称(假设用户输入正确)然后程序应该读取文本文件。我已经正确地完成了我程序的其他部分，但问题是当我再次输入名称时，它就是找不到文本文件，尽管它们在同一个文件夹中。

public static ArrayList<DogShop> readFile()
    {

        try 
        {   // The name of the file which we will read from
            String filename = "a.txt";

            // Prepare to read from the file, using a Scanner object
            File file = new File(filename);
            Scanner in = new Scanner(file);

            ArrayList<DogShop> shops = new ArrayList<DogShop>();

            // Read each line until end of file is reached
            while (in.hasNextLine())
            {
                // Read an entire line, which contains all the details for 1 account
                String line = in.nextLine();

                // Make a Scanner object to break up this line into parts
                Scanner lineBreaker = new Scanner(line);



                // 1st part is the account number
                try 
                {   int shopNumber = lineBreaker.nextInt();

                    // 2nd part is the full name of the owner of the account
                    String owner = lineBreaker.next();

                    // 3rd part is the amount of money, but this includes the dollar sign
                    String equityWithDollarSign = lineBreaker.next();

                    int total = lineBreaker.nextInt();

                    // Get rid of the dollar sign;
                    // we use the subtring method from the String class (see the Java API),
                    // which returns a new string with the first 'n' characters chopped off,
                    // where 'n' is the parameter that you give it
                    String equityWithoutDollarSign = equityWithDollarSign.substring(1);

                    // Convert this balance into a double, we need this because the deposit method
                    // in the Account class needs a double, not a String
                    double equity = Double.parseDouble(equityWithoutDollarSign);

                    // Create an Account belonging to the owner we found in the file
                    DogShop s = new DogShop(owner);



                    // Put money into the account according to the amount of money we found in the file
                    s.getMoney(equity);

                        s.getDogs(total);

                    // Put the Account into the ArrayList
                    shops.add(s);
                }

                catch (InputMismatchException e)
                {
                    System.out.println("File not found1.");

                }

                catch (NoSuchElementException e)
                {
                    System.out.println("File not found2");

                }

            }



        }


        catch (FileNotFoundException e)
        {
            System.out.println("File not found");

        }   // Make an ArrayList to store all the accounts we will make








        // Return the ArrayList containing all the accounts we made
        return shops;
    }

Answer 1

如果您在某些 IDE(如 Eclipse 或 NetBeans)中工作，您应该在项目的根目录中拥有该 a.txt 文件。 (而不是在构建 .class 文件的文件夹中或其他任何地方)

如果没有，您应该指定该文件的绝对路径。

---

编辑:
您可以将 .txt 文件与 .class(通常也是 .java 文件放在同一位置，因为您在同一文件夹中编译) 编译文件，如果你用 javac 手动编译它。这是因为它使用了相对路径，路径告诉JVM可执行文件所在的路径。

如果您使用某些 IDE，它会使用 Makefile 或类似 Windows 的东西为您生成编译后的文件，并将其视为默认文件结构，因此他知道相对路径从项目的根文件夹开始。