Save ArrayList to File and searchfor matching IDs

Question

I'm trying to make a program where the user enters personal info to a form which gets saved as an ArrayList object with String variables and saves it to a file. I want this file to be saved even when the program is closed, and when a new person enters their info it creates a new ArrayList and appends into the file.

My problem is trying to make a "search" function that lets you search your ID number and figures out if you're information is already in the file. This is my ActionListener method:

public void actionPerformed(ActionEvent e)
        {
            strID = tfID.getText();
            strName = tfName.getText();
            strYear = tfYear.getText();
            strSubject = tfSubject.getText();
            dblGPA = Double.parseDouble(tfGPA.getText());
            strComment = tfComment.getText();
            Student newStudent = new Student(strID, strName, strYear, strSubject, dblGPA, strComment);
            ArrayList<Student> studentInfo = new ArrayList<Student>();
            studentInfo.add(newStudent);
            try {
                writeFile(studentInfo);
                System.out.println(loadFile().toString());
            } catch (IOException e1) {
                e1.printStackTrace();
            } catch (ClassNotFoundException e1) {
                e1.printStackTrace();
            }       
        }

Then my Write and Read methods:

    public static void writeFile(ArrayList<Student> studentInfo) throws IOException {

    FileOutputStream fos = new FileOutputStream(new File("studentlog.dat"), true);
    ObjectOutputStream oos = new ObjectOutputStream(fos);
    oos.writeObject(studentInfo);
    oos.close();
}

public static ArrayList<Student> loadFile() throws IOException, ClassNotFoundException {

    FileInputStream fis = new FileInputStream(new File("studentlog.dat"));
    ObjectInputStream ois = new ObjectInputStream(fis);
    ArrayList<Student> sAL = (ArrayList<Student>) ois.readObject();
    ois.close();
    return sAL;
}

Now I just need an ActionListener method for a search button that will search the ID number from the JTextField tfSearch, then compare it to existing ID numbers in the file. I feel like I'm doing something horribly wrong but it could just be a dumb mistake.

Answer 1

If you're using a Listyou have to iterate over it to check if an object with a certain ID exists.

If you're using a Map<String, Student> (as mentioned by Andres), where the key of the map is your ID, you can easily use containsKey(String id)

Answer 2

Instead of an ArrayList, use a Map where the key is the id, and the value is the student. That will simplify the searchs a lot.

Map<String, Student> studentMap = new HashMap<String, Student>()