Question

谢谢你耐心等待。我想在重新发布之前尝试一些事情。我更改了代码以从文件中提取信息，使用arraylist编辑信息并将更新的信息写入“new”.dat文件。（对不起格式，不知道为什么有些代码粘贴在代码编辑器上面......）

公共类UserDeletedStudentFile { 学生信息学生信息; //声明一个StudentInformation对象 CollectStudentInformation文件; //声明一个CollectStudentInformation对象

// This constructor makes a copy of the StudentInformation object passed by the infoObject argument...
public UserDeletedStudentFile(StudentInformation infoObject)
{
    studentInfo = new StudentInformation(infoObject);
}

// This no-arg constructor allows access from the DemoStudentAdmin.java class...
public UserDeletedStudentFile() {};

// getStudentInformation() returns a copy of the StudentInformation object with student name and ID number...
public StudentInformation getStudentInformation()
{   return new StudentInformation(studentInfo);   } 

// deleteStudentFile() deletes a student file as needed by the user...
public void deleteStudentFile() throws IOException
{
    String userInput = "";          // For user input
    int userToFileTransition = 0;   // Subracting one from the user's choice to read the record needed
    int selectionNumber = 0;        // Number for user to choose
    int indexNumber = 0;

    // Open a new studentDirectory.dat and populate the ArrayList<>...
    file = new CollectStudentInformation("studentFileDirectory.dat");

    // Create an ArrayList<>...
    ArrayList<StudentInformation> studentFiles = new ArrayList<>();

    // Populate the ArrayList<> with the information from the StudentInformation class...
    for(int y = 0; y < file.getNumberOfRecords(); y++)
    {
        file.moveFilePointer(y);
        studentInfo = file.readStudentFile();
        studentFiles.add(studentInfo);
    } 

    // Ask the user if they wish to see one record, all records of currently enrolled students or Quit the menu option...
    while(selectionNumber < 1 || selectionNumber > 3)
    {
        userInput = JOptionPane.showInputDialog(null, "\n\nPlease choose from one of the following options:" +
                                                      "\nPress '1' for the student record number" +
                                                      "\nPress '2' for the Mars University directory" +
                                                      "\nPress '3' to return to the main menu.");
        selectionNumber = Integer.parseInt(userInput);
    }

    // Display the selection choices...
    if(selectionNumber == 1)
    {
        // Get a record number from the user, subtract 1 and display...
        userInput = JOptionPane.showInputDialog(null, "Enter the record number you wish to delete: "); 
        userToFileTransition = Integer.parseInt(userInput);
        indexNumber = (userToFileTransition - 1);              // pulling from the array, not the random access file...

        // Read the record at that location...
        studentInfo = studentFiles.get(indexNumber);

        // Display the student information for the user to verify...
        System.out.println("\n" + studentInfo.getfirstName());
        System.out.println(studentInfo.getLastName());
        System.out.println(studentInfo.getStudentID());

        // Remove the student file...
        studentFiles.remove(indexNumber);

        // Testing for the correct number of elements in the arrayList...
        for(StudentInformation student : studentFiles) 
            System.out.println(student);

        //Create an CollectStudentInformation object...
        file = new CollectStudentInformation("studentFileDirectory.dat");

        for(int x = 0; x < studentFiles.size(); x++)
            file.writeStudentFile(studentFiles.get(x));
    }

    // Clear the ArrayList<> of all values...
    studentFiles.clear();

    // close the file...
    file.close();

    // Return to the main() to access the menu...              
    DemoStudentAdmin.main(null);

所以...每个类（创建，读取，修改和删除）都以相同的方式创建，只有'Delete'类没有编写更新的ArrayList（studentFiles）。相反，它将删除请求的对象并将该元素替换为以下对象的副本。 trimToSize（）在这个实例中也不起作用。

再次感谢您的帮助！

从随机访问文件中删除类对象并用Java“重写”该文件

0 个答案: