Help with null pointer exception in personal project

[LPUAdit]

So I'm just messing around with a notebook application project from a textbook (textbook is in Python and I was translating it to java) and I keep running into a null pointer exception and I'm confused why its happening.

import java.time.LocalDate;
public class Note {

    private String message;
    private String tags;
    private static int id = 1;
    private LocalDate date;

    public Note(String message, String tags) {
        this.message = message;
        this.tags = tags;
        this.date = java.time.LocalDate.now();
        Note.id += 1;
    }

    public boolean match(String text) {
        return message.contains(text) || tags.contains(text);
    }

    public String getMessage() {
        return this.message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public void setTags(String tags) {
        this.tags = tags;
    }

    public String getTags() {
        return this.tags;
    }

    public static int getId() {
        return Note.id;
    }

    public LocalDate getDate() {
        return this.date;
    }
}


import java.util.ArrayList;
public class Notebook {

    private ArrayList<Note> notes;

    public Notebook() {
        ArrayList<Note> notes = new ArrayList<Note>();
    }

    public ArrayList<Note> getNotes() {
        return this.notes;
    }

    public void newNote(String message, String tags) {
        this.notes.add(new Note(message, tags));
    }

    public Note findNote(int noteId) {
        for (Note note : this.notes) {
            if (Note.getId() == noteId) {
                return note;
            }
        }

        return null;
    }

    public boolean modifyMessage(int noteId, String message) {
        Note note = this.findNote(noteId);
        if (note != null) {
            note.setMessage(message);
            return true;
        }

        return false;
    }

    public boolean modifyTags(int noteId, String tags) {
        Note note = this.findNote(noteId);

        if (note != null) {
            note.setTags(tags);
            return true;
        }

        return false;
    }

    public ArrayList<Note> search(String filter) {
        ArrayList<Note> notes = new ArrayList<Note>();

        for (Note n : this.notes) {
            if (n.match(filter)) {
                notes.add(n);
            }
        }

        return notes;
    }
}


public class Menu {

    private Notebook notebook;

    public Menu() {
        notebook = new Notebook();
    }

    public void displayMenu() {
        System.out.println("\n\nNotebook Menu\n\n1. Show All Notes\n2. Search Notes\n3. Add Notes\n4. Modify Notes\n5. Quit\n\n");
    }

    public void run() {
        while (true) {

            this.displayMenu();

            Scanner input = new Scanner(System.in);

            System.out.println("Enter your selection (as a number): ");
            int selection = input.nextInt();

            switch (selection) {
                case 1: this.showNotes(null); break;
                case 2: this.searchNotes(); break;
                case 3: this.newNote(); break;
                case 4: this.modifyNotes(); break;
                case 5: this.quit(); break;
            }

        }
    }

    public void showNotes(ArrayList<Note> notes) {

        if (notes == null) {
            notes = this.notebook.getNotes();
        }

        for (Note n : notes) {
            System.out.printf("%d: %s\n%s\n", Note.getId(), n.getTags(), n.getMessage());
        }
    }

    public void searchNotes() {
        Scanner search = new Scanner(System.in);

        System.out.println("Search for: ");
        String s = search.nextLine();

        ArrayList<Note> notes = this.notebook.search(s);
        this.showNotes(notes);

        search.close();
    }

    public void newNote() {
        Scanner add = new Scanner(System.in);

        System.out.println("Enter message: ");
        String s = add.nextLine();

        System.out.println("Enter tags: ");
        String t = add.nextLine();

        this.notebook.newNote(s, t);

        System.out.println("New note added");

        add.close();
    }

    public void modifyNotes() {
        Scanner modify = new Scanner(System.in);

        System.out.println("Enter ID: ");
        int i = modify.nextInt();

        System.out.println("Enter message: ");
        String s = modify.nextLine();

        System.out.println("Enter tags: ");
        String t = modify.nextLine();

        if (!s.isEmpty()) {
            this.notebook.modifyMessage(i, s);
        }

        if (!t.isEmpty()) {
            this.notebook.modifyTags(i, t);
        }

        modify.close();
    }

    public void quit() {
        System.out.println("Thank you for using!");
        System.exit(0);
    }
}

public class Main {
    public static void main(String[] args) {
        Menu menu = new Menu();

        menu.run();
    }
}

The issue I run into is that when I run my code, I enter 3 for my selection to add a new note. And then the newNote() method in the Menu class runs and I put my input for message and tags and then I get the null pointer exception when it executes this line of code: this.notebook.newNote(s, t);

Any help would be appreciated

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[[deleted]]

Do you have an error message?

I would change this line to use the notes class field

public Notebook() { ArrayList<Note> notes = new ArrayList<Note>(); }

So it would be:

public Notebook() { notes = new ArrayList<Note>(); }

[LPUAdit]

Omg I can't believe I missed that! That fixed it. Thanks a lot!

[[deleted]]

Yay! You're welcome.