java - 文件输入输出追加

Question

我正在尝试将一些坐标写入文件，然后将其作为字符串读取。所以我需要将它们写入附加文件......没有空格或换行，但我的代码只写入第一个坐标，即 pos_Let ，但不写入 pos_Num code> 根本没有，甚至没有空格或换行。

那么我怎样才能得到像这样写入文件 pos_LetposNum 的代码呢？显然我的意思是他们的引用文献;) ..提前致谢

protected  void writeCoordtoFile () throws IOException
  {
       File file = new File("FermiPresentCoord.txt");
       boolean yes = file.createNewFile() ;
       //boolean yes = exists();
       if (yes == true)
       {
       // create a FileWriter Object
       FileWriter writer = new FileWriter(file, true);

       // Writes the content to the file
       writer.write("");
       writer.flush();
       writer.write(pos_Let);
       writer.flush();
       writer.write(pos_Num);
       writer.close();
       }
       else
       {
           // creates the file
           file.createNewFile();

           // creates a FileWriter Object
           FileWriter out = new FileWriter(file);

           // Writes the content to the file
           out.write(pos_Let);
           out.flush();
           out.write(pos_Num);
           out.flush();
           out.close();
       }
  }  

Answer 1

引用方法createNewFile() :

Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist. The check for the existence of the file and the creation of the file if it does not exist are a single operation that is atomic with respect to all other filesystem activities that might affect the file.

Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably. The FileLock facility should be used instead.

Returns:true if the named file does not exist and was successfully created; false if the named file already exists

在您的情况下，您首先创建文件，并且 createNewFile() 返回 true，因此您转到 if block ，将该行附加到当前文件。然后，createNewFile() 返回 false，因为该文件存在!因此，您转到 else block ，然后从头开始重新创建文件...

所以，基本上，只需用 else 反转 if，并且不要调用 createNewFile() 两次...可能的更改(这样您就不会感到困惑)这是我的简单建议:

protected  void writeCoordtoFile () throws IOException
{
   File file = new File("FermiPresentCoord.txt");
   boolean fileDoesNotExist = file.createNewFile() ;
   //boolean fileDoesNotExist = file does **not** exist!
   if (fileDoesNotExist)
   {
       // create a FileWriter Object
       FileWriter writer = new FileWriter(file);

       // Writes the content to the file
       writer.write(pos_Let);
       writer.write(pos_Num);
       writer.close();
       
   }
   else
   {
       // creates a FileWriter Object
       FileWriter out = new FileWriter(file,true);

       // Writes the content to the file
       out.write(""); //not sure why you need that...
       out.write(pos_Let);
       out.write(pos_Num);
       out.close();
   }
}