writeToFile写入文件两次

Question

我已经尝试out.append(s);然而我的问题已经失去控制。还有别人看到我的眼睛不见了吗？

public void writeToFile()
{
    PrintWriter out = null;
    try
    {
        out = new PrintWriter(new BufferedWriter(new FileWriter("course.txt", true)));

        for (String courseName:courseData.keySet())
        {
            Course course = courseData.get(courseName);
            if (!course.isEmpty())
            {
                ArrayList<String> students = course.getStudentList();
                for (String s : students)
                {                        
                    out.println(courseName + "<<<<" + s);                                             
                }
            }
            else
            {
                out.println(courseName + "<<<<");

            }



        }
    } catch (IOException ex)
    {
        Logger.getLogger(CourseApp.class.getName()).log(Level.SEVERE, null, ex);
    }
    finally
    {
        out.close();
    }
}

我输入后，我的文本文件应如下所示。

然而，这是我实际得到的结果。