Question

当我运行此方法时，我收到“null”，为什么？下面是代码。我没有超类，因为我的作业只需要子类，其中一个是验证文件所必需的/如果需要则创建它。这也恰好是我最难解决的问题。

System.out.print("Welcome to My Statistics Calculator"
        + "\nEnter the name of your text file (e.g. MyNumbers)"
        + "\nThe file extension will be added after entry."
        + "->: ");
String fn = input.nextLine();
String fileN = fn + ".txt";
String directFile = "C:\\W12Assignment\\" + fileN;

//calling subclass toValidate
toValidate vali = new toValidate(fileN, directFile);
System.out.println(vali.getValidDirect());
System.out.println(vali.getValidFile());

这是我的子类：

public class toValidate extends W12Assignment {
    //constructors
    private String fileN;
    private File FN;
    private String directFile;
    private File directory;

    public toValidate(String fiNa, String dire) {
        fileN = fiNa;
        directFile = dire;

        //calling methods
        setValidFile(fileN);
        setValidDirect(directFile);

    }

    public File getValidFile() {
        return FN;
    }

    public File getValidDirect() {
        return directory;
    }

    private File setValidFile(String fileN) throws IOException {
        File FN = new File(fileN);
        if (!FN.exists()) {
            System.out.println("The file does not exist.\nCreating file...");
            FN.createNewFile();
            System.out.printf("The file now exists and is located here:\n%s\n",
                    FN.getAbsolutePath());
        } else {
            System.out.printf("The file already exists and is located here:\n%s\n",
                    FN.getAbsolutePath());
        }
        return FN;
    }

    private File setValidDirect(String directFile) {
        File directory = new File(directFile);
        if (!directory.exists()) {
            directory.mkdirs();
            System.out.println("The directory does not exist.\nCreating directory...");
        } else {
            System.out.printf("The directory does exist at this location: \n%s\n",
                    directory.getAbsolutePath());
        }
        return directory;
    }
}

Answer 1

看来您正在使用方法变量隐藏类变量。尝试改变

File FN = new File(fileN);

到

 FN = new File(fileN);

在你的方法 setValidFile（）

上

当我调用此方法时，为什么会出现“null”？这是关于文件验证

1 个答案: