打印到文件的更改未保存

Question

try{


 private fileWriter= new PrintWriter(new FileWriter(file.txt));
                fileWriter.print("hello world");
                System.out.println("file written");

                fileWriter.close();
}
catch (IOException e){
            e.printStackTrace();

        } finally {
        }

I have this text file in my source folder. So far, there haven't been any errors with accessing it. However, when I close the program or after when the files should have been written when I open the text file I don't find them there, however I did check the bin folder ocne and it seemed to print hello world to the temp copy there.

I want the changes it makes to be permanent.

Answer 1

You have a couple of problems in your code. Correcting/simplifying it to the following:

public static void main(String[] args) throws IOException {
    PrintWriter fileWriter = new PrintWriter(new FileWriter(new File("file.txt")));
    fileWriter.print("hello world");
    System.out.println("file written");
    fileWriter.close();
}

makes it create the file as expected. Try that out, and if it doesn't behave the way you're expecting, then explain how. Note that when you give a relative file path, it resolves the path against your current working directory. If the file is being written somewhere you don't expect, this is probably why.

Answer 2

The file in the bin folder is not a temp file, it is the file you are actually writing. If you want to write to the file in the source folder you have to use it's correct file path when opening the file for writing. Java always computes relative paths to the folder you started your application in. So your application is probably started in the bin folder and writes to file.txt there.

Answer 3

Maybe try using the append boolean in the FileWriter constructor

public FileWriter(String fileName, boolean append)

...and I think eclipse will use the bin folder as its default classpath so its no surprise the file is written there.

I hope that helps :)

Answer 4

由于代码可以很好地进入包资源管理器 - >项目 - >属性 - > java构建路径 - >源代码 - >选中“允许源文件夹输出”的复选框