HallLedger Developer Guide

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Acknowledgements

• HallLedger’s demerit rule catalogue is adapted from the NUS Office of Student Affairs Demerit Point Structure (DPS) for Breach of Housing Agreement, dated 9 January 2026.
• This project is based on the AddressBook-Level3 (AB3) codebase from se-education/addressbook-level3.

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Setting up, getting started

Refer to the guide Setting up and getting started.

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Design

Architecture

The Architecture Diagram given above explains the high-level design of the App.

Given below is a quick overview of main components and how they interact with each other.

Main components of the architecture

Main (consisting of classes Main and MainApp) is in charge of the app launch and shut down.

• At app launch, it initializes the other components in the correct sequence, and connects them up with each other.
• At shut down, it shuts down the other components and invokes cleanup methods where necessary.

The bulk of the app's work is done by the following four components:

• UI: The UI of the App.
• Logic: The command executor.
• Model: Holds the data of the App in memory.
• Storage: Reads data from, and writes data to, the hard disk.

Commons represents a collection of classes used by multiple other components.

How the architecture components interact with each other

The Sequence Diagram below shows how the components interact with each other for the scenario where the user issues a delete command.

Each of the four main components (also shown in the diagram above),

• defines its API in an interface with the same name as the Component.
• implements its functionality using a concrete {Component Name}Manager class (which follows the corresponding API interface mentioned in the previous point.

For example, the Logic component defines its API in the Logic.java interface and implements its functionality using the LogicManager.java class which follows the Logic interface. Other components interact with a given component through its interface rather than the concrete class (reason: to prevent outside component's being coupled to the implementation of a component), as illustrated in the (partial) class diagram below.

The sections below give more details of each component.

UI component

The API of this component is specified in Ui.java

The UI consists of a MainWindow that is made up of parts e.g.CommandBox, ResultDisplay, TabSection, ListSection etc. All these, including the MainWindow, inherit from the abstract UiPart class which captures the commonalities between classes that represent parts of the visible GUI.

The UI component uses the JavaFx UI framework. The layout of these UI parts are defined in matching .fxml files that are in the src/main/resources/view folder. For example, the layout of the MainWindow is specified in MainWindow.fxml

The UI component,

• executes user commands using the Logic component.
• listens for changes to Model data so that the UI can be updated with the modified data.
• keeps a reference to the Logic component, because the UI relies on the Logic to execute commands.
• depends on some classes in the Model component, as it displays Person objects residing in the Model.

Logic component

API : Logic.java

Here's a (partial) class diagram of the Logic component:

The sequence diagram below illustrates the interactions within the Logic component, taking a delete command as an example.

How the Logic component works:

1. When Logic is called upon to execute a command, it is passed to an AddressBookParser object which in turn creates a parser that matches the command (e.g., DeleteCommandParser) and uses it to parse the command.
2. This results in a Command object (more precisely, an object of one of its subclasses e.g., DeleteCommand) which is executed by the LogicManager.
3. The command can communicate with the Model when it is executed (e.g. to delete a person).
   Note that although this is shown as a single step in the diagram above (for simplicity), in the code it can take several interactions (between the command object and the Model) to achieve.
4. The result of the command execution is encapsulated as a CommandResult object which is returned back from Logic.

Here are the other classes in Logic (omitted from the class diagram above) that are used for parsing a user command:

How the parsing works:

• When called upon to parse a user command, the AddressBookParser class creates an XYZCommandParser (XYZ is a placeholder for the specific command name e.g., AddCommandParser) which uses the other classes shown above to parse the user command and create a XYZCommand object (e.g., AddCommand) which the AddressBookParser returns back as a Command object.
• All XYZCommandParser classes (e.g., AddCommandParser, DeleteCommandParser, ...) inherit from the Parser interface so that they can be treated similarly where possible e.g., during testing.

Model component

API : Model.java

The Model component,

• stores the address book data i.e., all Person objects (which are contained in a UniquePersonList object).
• stores the currently 'selected' Person objects (e.g., results of a search query) as a separate filtered list which is exposed to outsiders as an unmodifiable ObservableList<Person> that can be 'observed' e.g. the UI can be bound to this list so that the UI automatically updates when the data in the list change.
• stores a UserPref object that represents the user’s preferences. This is exposed to the outside as a ReadOnlyUserPref object.
• does not depend on any of the other three components (as the Model represents data entities of the domain, they should make sense on their own without depending on other components)

Storage component

API : Storage.java

The Storage component,

• can save both address book data and user preference data in JSON format, and read them back into corresponding objects.
• inherits from both AddressBookStorage and UserPrefStorage, which means it can be treated as either one (if only the functionality of only one is needed).
• depends on some classes in the Model component (because the Storage component's job is to save/retrieve objects that belong to the Model)

Common classes

Classes used by multiple components are in the seedu.address.commons package.

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Implementation

This section describes some noteworthy details on how certain features are implemented.

Demerit point tracking

HallLedger stores demerit incidents as resident-level records instead of storing only a mutable running total.

Each demerit incident records:

• the DPS rule index,
• the rule title,
• the offence number for that resident and rule,
• the points applied for that occurrence,
• and an optional remark.

The resident’s total demerit points are derived by summing the points applied across all stored demerit incidents. This avoids duplicated derived state and keeps the resident’s demerit history auditable.

The demerit feature is split into two user-facing commands:

• demeritlist — displays the indexed demerit rule catalogue and point tiers.
• demerit — applies an indexed demerit rule to a resident identified by student ID.

Rationale for the current design

A resident may commit the same rule multiple times, and the DPS applies different point tiers based on repeated occurrences. Hence, storing only a running total would lose important context such as:

• which rule was applied,
• how many times it has already been committed by that resident,
• and what exact points were awarded for that occurrence.

By storing incidents individually, HallLedger can:

• reconstruct total demerit points at any time,
• preserve a readable incident history,
• and support future enhancements such as warnings, alerts, or administrative review.

Current scope note

HallLedger currently records resident demerit incidents and computes accumulated totals. It does not yet automatically enforce semester-based or lifetime housing sanctions tied to DPS thresholds.

[Proposed] Undo/redo feature

Proposed Implementation

The proposed undo/redo mechanism is facilitated by VersionedAddressBook. It extends AddressBook with an undo/redo history, stored internally as an addressBookStateList and currentStatePointer. Additionally, it implements the following operations:

• VersionedAddressBook#commit() — Saves the current address book state in its history.
• VersionedAddressBook#undo() — Restores the previous address book state from its history.
• VersionedAddressBook#redo() — Restores a previously undone address book state from its history.

These operations are exposed in the Model interface as Model#commitAddressBook(), Model#undoAddressBook() and Model#redoAddressBook() respectively.

Given below is an example usage scenario and how the undo/redo mechanism behaves at each step.

Step 1. The user launches the application for the first time. The VersionedAddressBook will be initialized with the initial address book state, and the currentStatePointer pointing to that single address book state.

Step 2. The user executes a delete command to delete a resident in the address book. The delete command calls Model#commitAddressBook(), causing the modified state of the address book after the command executes to be saved in the addressBookStateList, and the currentStatePointer is shifted to the newly inserted address book state.

Step 3. The user executes an add command to add a new resident. The add command also calls Model#commitAddressBook(), causing another modified address book state to be saved into the addressBookStateList.

Step 4. The user now decides that adding the resident was a mistake, and decides to undo that action by executing the undo command. The undo command will call Model#undoAddressBook(), which will shift the currentStatePointer once to the left, pointing it to the previous address book state, and restores the address book to that state.

The following sequence diagram shows how an undo operation goes through the Logic component:

Similarly, how an undo operation goes through the Model component is shown below:

The redo command does the opposite — it calls Model#redoAddressBook(), which shifts the currentStatePointer once to the right, pointing to the previously undone state, and restores the address book to that state.

Step 5. The user then decides to execute the command list. Commands that do not modify the address book, such as list, will usually not call Model#commitAddressBook(), Model#undoAddressBook() or Model#redoAddressBook(). Thus, the addressBookStateList remains unchanged.

Step 6. The user executes clear, which calls Model#commitAddressBook(). Since the currentStatePointer is not pointing at the end of the addressBookStateList, all address book states after the currentStatePointer will be purged. Reason: It no longer makes sense to redo the earlier add command. This is the behavior that most modern desktop applications follow.

The following activity diagram summarizes what happens when a user executes a new command:

Design considerations:

Aspect: How undo & redo executes:

• Alternative 1 (current choice): Saves the entire address book.

  • Pros: Easy to implement.
  • Cons: May have performance issues in terms of memory usage.

• Alternative 2: Individual command knows how to undo/redo by itself.

  • Pros: Will use less memory (e.g. for delete, just save the person being deleted).
  • Cons: We must ensure that the implementation of each individual command is correct.

{more aspects and alternatives to be added}

[Proposed] Data archiving

{Explain here how the data archiving feature will be implemented}

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Documentation, logging, testing, configuration, dev-ops

• Documentation guide
• Testing guide
• Logging guide
• Configuration guide
• DevOps guide

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Appendix: Requirements

Product scope

HallLedger is a desktop application for Resident Assistants (RAs) and other hall administrators who need to manage resident contact records quickly and accurately. It is optimized for hall-level resident administration, where users frequently need to search, update, and maintain resident details such as student ID, room assignment, contact information, and emergency contact details.

Beyond basic resident record management, HallLedger is intended to support common hall-administration workflows such as tagging residents by attributes (e.g. year of study, major, gender), monitoring occupancy at the room level, tracking demerit incidents, and serving as a foundation for future hall-management features such as retention-related review and other resident administration tasks.

HallLedger is not intended to replace university-wide housing allocation systems, payment systems, or institutional access-control systems. Its scope is limited to block-level or hall-level resident management and operational tracking.

Target user profile:

• has a need to manage a significant number of resident records within a hall or block
• is a Resident Assistant (RA), hall administrator, or student leader handling resident administration
• frequently needs to search for residents by name, student ID, room number, or tagged attributes
• needs quick access to resident contact details and emergency contacts
• prefers a desktop app over manual spreadsheets or scattered notes
• can type fast
• prefers typing to mouse interactions
• is reasonably comfortable using CLI-style commands

Value proposition: HallLedger helps hall administrators manage resident records faster and with fewer errors than spreadsheets or manual lists, while providing a centralized and command-driven workflow tailored to hall operations.

User stories

Priorities: High (must have) - * * *, Medium (nice to have) - * *, Low (unlikely to have) - *

{More to be added}

Use cases

(For all use cases below, the System is HallLedger and the Actor is the Residential Assistant (RA), unless specified otherwise)

Use case: UC01 - Add a new student

MSS

1. RA requests to add a new student, providing the student's details (e.g., name, phone, email, room number, tags).
2. HallLedger adds the new student.
3. HallLedger displays a success message with the added student's details.

Use case ends.

Extensions

• 1a. RA provides an invalid format for the details (e.g., incorrect phone number format).

  • 1a1. HallLedger shows an error message indicating the correct format. Use case resumes from step 1.

• 1b. A student with the exact same details already exists in the system.

  • 1b1. HallLedger indicates that the student already exists. Use case ends.

• 1c. RA fails to provide compulsory details (name, phone, email, room number).

  • 1c1. HallLedger shows an error message indicating the compulsory details. Use case resumes from step 1.

Use case: UC02 - View a student's details (basic info, demerit records)

MSS

1. RA requests to list all students.
2. HallLedger shows a list of students.
3. RA identifies a specific student from the list.
4. HallLedger displays the student's basic information and current demerit total in the UI.

Use case ends.

Extensions

• 2a. The student list is empty.
  • 2a1. HallLedger indicates that the student list is empty. Use case ends.

Use case: UC03 - Edit a student's info

MSS

1. RA requests to edit specific details (e.g., phone, email, room number, tags) of a student using their student ID.
2. HallLedger updates the student's details.
3. HallLedger displays a success message with the updated student's details.

Use case ends.

Extensions

• 1a. The given student ID does not exist.

  • 1a1. HallLedger shows an error message indicating that the student was not found. Use case ends.

• 1b. RA provides an invalid format for the details to be updated.

  • 1b1. HallLedger shows an error message indicating the correct format. Use case resumes from step 1.

• 1c. RA provides details that are exactly the same as the existing ones, resulting in no changes. Use case resumes from step 1.

Use case: UC04 - Delete or Clear student records

MSS

1. RA requests to delete a specific student or clear all current student records.
2. HallLedger deletes the specified student or clears all data.
3. HallLedger displays a success message reflecting the changes.

Use case ends.

Extensions

• 1a. The student list is already empty. Use case ends.

• 1b. If deleting, the given student ID is invalid.

  • 1b1. HallLedger shows an error message. Use case resumes from step 1.

Use case: UC05 - Search and filter students

MSS

1. RA requests to search by name or filter by specific attributes (e.g., room, year, tags).
2. HallLedger processes the query.
3. HallLedger shows a list of matching students.

Use case ends.

Extensions

• 1a. RA provides empty keywords or invalid criteria format.

  • 1a1. HallLedger shows an error message indicating how to use the specific command correctly. Use case ends.

• 2a. No students match the given criteria.

  • 2a1. HallLedger shows an empty list and indicates that 0 students were found. Use case ends.

Use case: UC06 - Add a demerit record

MSS

1. RA requests to list the available demerit rules.
2. HallLedger displays the indexed demerit rule catalogue.
3. RA requests to add a demerit record to a specific student using the student's ID and the rule index.
4. HallLedger records the demerit incident for that student.
5. HallLedger updates the resident's total demerit points.
6. HallLedger displays a success message showing the applied rule and updated total.

Use case ends.

Extensions

• 1a. No demerit rules are available.

  • 1a1. HallLedger displays an empty result. Use case ends.

• 3a. The given student ID is invalid.

  • 3a1. HallLedger shows an error message indicating that the student was not found. Use case resumes at step 2.

• 3b. The given rule index does not exist.

  • 3b1. HallLedger shows an error message indicating that the rule index is invalid. Use case resumes at step 2.

Use case: UC07 - Export data

MSS

1. RA requests to export all student details data to a CSV file.
2. HallLedger gathers the relevant data.
3. HallLedger exports the file to the user's system.

Use case ends.

Extensions

• 1a. The student list is empty.
  • 1a1. HallLedger indicates that there is no data to generate a report or export. Use case ends.

Non-Functional Requirements

1. Should work on any mainstream OS as long as it has Java 17 or above installed.

2. Should be able to store up to 1000 students without noticeable sluggishness in performance for typical usage.

3. Should have a response time of < 2 seconds for all instructions.

4. A user with above-average typing speed for regular English text (i.e., not code, not system admin commands) should be able to accomplish most tasks faster using commands than using the mouse.

5. Interaction with the product should be intuitive even for non-technical users, e.g., simple error messages should be displayed and help should be easily available when needed.

6. The product is not required to handle more than one user at a time.

7. The product should be free to use and open source.

8. The product should not need an internet connection to use.

Glossary

• Hall : A residential building on campus that houses students. Each hall is made up of multiple blocks, and each block is made up of multiple rooms.
• RA : Resident Assistant, a student leader who is responsible for managing a block of rooms in a hall and the students living in those rooms.
• CCA : Co-Curricular Activities, which are activities that students participate in outside of their academic curriculum.
• DPS : Demerit Point Structure used as the source reference for HallLedger’s demerit rule catalogue.
• Mainstream OS : Windows, Linux, Unix, macOS.
• Non-technical users : Users who are not familiar with technical jargon, command-line interfaces, or programming concepts.

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Appendix: Instructions for manual testing

Given below are instructions to test the app manually.

Launch and shutdown

1. Initial launch

   1. Download the jar file and copy it into an empty folder.

   2. Double-click the jar file.
      Expected: Shows the GUI with a set of sample contacts. The window size may not be optimum.

2. Saving window preferences

   1. Resize the window to an optimum size. Move the window to a different location. Close the window.

   2. Re-launch the app by double-clicking the jar file.
      Expected: The most recent window size and location is retained.

Deleting a person

1. Deleting a person while all persons are being shown

   1. Prerequisites: List all persons using the list command. Multiple persons in the list.

   2. Test case: delete i=A1234567X
      Expected: The matching resident is deleted from the list. Details of the deleted resident are shown in the status message. Timestamp in the status bar is updated.

   3. Test case: delete i=A0000000Z
      Expected: No person is deleted. Error details shown in the status message. Status bar remains the same.

   4. Other incorrect delete commands to try: delete, delete x, delete i=notAStudentId
      Expected: Similar to previous.

Demerit commands

1. Listing demerit rules

   1. Test case: demeritlist
      Expected: The result box shows the indexed demerit rule catalogue.

2. Adding a demerit record

   1. Prerequisites: At least one resident exists in the list.

   2. Test case: demerit i=A1234567X di=18
      Expected: A success message is shown. The resident's displayed demerit total increases according to the first-offence tier of rule 18.

   3. Test case: Repeat demerit i=A1234567X di=18
      Expected: A success message is shown. The resident's displayed demerit total increases again according to the next offence tier.

   4. Test case: demerit i=A9999999Z di=18
      Expected: No demerit is added. An error message is shown indicating that the resident was not found.

   5. Test case: demerit i=A1234567X di=999
      Expected: No demerit is added. An error message is shown indicating that the rule index does not exist.

Saving data

1. Dealing with missing/corrupted data files

   1. Delete or rename the data/addressbook.json file, then relaunch the app.
      Expected: HallLedger starts with sample data or an empty initialized data file instead of crashing.

   2. Edit data/addressbook.json into an invalid JSON format, then relaunch the app.
      Expected: HallLedger detects that the data file cannot be loaded and starts safely without using the corrupted data.