我想创建一个类来创建一个文件，并使用main类来检查该文件是否被创建，但我的代码失败了.(Java)

Question

public class Fileverifynanoha 
{
    private File fileext;
    private Path filepath;
    public Fileverifynanoha()//this class wants to create a file, write something, and close it.
{
    filepath = Paths.get("./txttest.txt");
    Charset charset = Charset.forName("US-ASCII");
    String s = "Takamachi Nanoha. Shirasaki Tsugumi.!";
    try (BufferedWriter filewriter = Files.newBufferedWriter(filepath,charset))
    {
        filewriter.write(s,0,s.length()-1);   
    }
    catch(IOException e)
         {
            System.err.println(e);
         }
}//end of this class
/**
 * @param args the command line arguments
 */
public static void main(String[] args)//the main method will check if this file contains(created), if so, return exist. if not, return doesnt exist.
{
    if (filetxt.exists()&&!filetxt.isDirectory())//object does not create any real thing, therefore nothing true will return.
    {
        System.out.println("File exist.");
    }
    else
    {
        System.out.println("File does not exist.");
    }
}
}

下面是代码。我想用我创建的类来创建一个文件，写一些东西。然后，我使用main类检查该文件是否存在。

然而，我不知道为什么，但是主类不识别我(可能)创建的文件。谁能告诉我怎么把它们联系起来?

我知道这个程序可能有一些小错误。我稍后会解决这个问题。

谢谢。

Answer 1

您从未调用过构造函数。

public static void main(String[] args)//the main method will check if this file contains(created), if so, return exist. if not, return doesnt exist.
{
    Fileverifynanoha fvn = new Fileverifynanoha();
    if (fvn.filetxt.exists()&&!fvn.filetxt.isDirectory())
    {
        System.out.println("File exist.");
    }
    else
    {
        System.out.println("File does not exist.");
    }
}
}

Answer 2

您的问题:

• 没有创建类的实例
• 没有初始化File file，所以总是null
纯文本文件最好使用utf-8。

试试这个:

import java.io.BufferedWriter;
import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
public class Fileverifynanoha {
    private File file;
    private Path path;
    public Fileverifynanoha(String fp) {
        this.path = Paths.get(fp);
        this.file = path.toFile();
    }
    public void createFile()// this class wants to create a file, write something, and close it.
    {
        Charset charset = Charset.forName("UTF-8");
        String s = "Takamachi Nanoha. Shirasaki Tsugumi.!";
        BufferedWriter filewriter = null;
        try {
            filewriter = Files.newBufferedWriter(path, charset);
            filewriter.write(s, 0, s.length() - 1);
            filewriter.close();
        } catch (IOException e) {
            System.err.println(e);
        }
    }// end of this class
    /**
     * @param args
     *            the command line arguments
     */
    public static void main(String[] args)// the main method will check if this file contains(created), if so, return exist. if not, return doesnt exist.
    {
        Fileverifynanoha f = new Fileverifynanoha("./txttest.txt");
        f.createFile();
        if (f.file.exists() && !f.file.isDirectory())// object does not create any real thing, therefore nothing true will return.
        {
            System.out.println("File exist.");
        } else {
            System.out.println("File does not exist.");
        }
    }
}