Folder

public class Folder implements Serializable {

    private int id;
    private String name;
    private ArrayList<Folder> subFolders;
    private Rule rule;
    private ArrayList<Message> messages;

    public Folder(int id, String name, Rule rule) {
        super();
        this.id = id;
        this.name = name;
        this.rule = rule;
        this.subFolders = new ArrayList<>();
        this.messages = new ArrayList<>();
    }

    public Folder(int id, String name, ArrayList<Folder> subFolders, Rule rule) {
        super();
        this.id = id;
        this.name = name;
        this.subFolders = subFolders;
        this.rule = rule;
        this.messages = new ArrayList<>();
    }

    public Folder(int id, String name, ArrayList<Folder> subFolders, Rule rule, ArrayList<Message> messages) {
        this.id = id;
        this.name = name;
        this.subFolders = subFolders;
        this.rule = rule;
        this.messages = messages;
    }

    public int getId() {
        return this.id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public ArrayList<Folder> getSubFolders() {
        return subFolders;
    }

    public void setSubFolders(ArrayList<Folder> subFolders) {
        this.subFolders = subFolders;
    }

    public Rule getRule() {
        return rule;
    }

    public void setRule(Rule rule) {
        this.rule = rule;
    }

    public ArrayList<Message> getMessages() {
        return messages;
    }

    public void setMessages(ArrayList<Message> messages) {
        this.messages = messages;
    }

    public void addMessage(Message message) {
        if (!messages.contains(message))
            messages.add(message);
    }

    public void removeMessage(Message message) {
        if (messages.contains(message))
            messages.remove(message);
    }

    @Override
    public String toString() {
        return "Folder{" +
                "name='" + name + '\'' +
                '}';
    }
}