PROJECT: AddressBook - Level 3

Overview

AddressBook - Level 3 is a desktop address book application used for teaching Software Engineering principles. The user interacts with it using a CLI, and it has a GUI created with JavaFX. It is written in Java, and has about 10 kLoC.

Summary of contributions

  • Major enhancement: added the ability to undo/redo previous commands

    • What it does: allows the user to undo all previous commands one at a time. Preceding undo commands can be reversed by using the redo command.

    • Justification: This feature improves the product significantly because a user can make mistakes in commands and the app should provide a convenient way to rectify them.

    • Highlights: This enhancement affects existing commands and commands to be added in future. It required an in-depth analysis of design alternatives. The implementation too was challenging as it required changes to existing commands.

    • Credits: {mention here if you reused any code/ideas from elsewhere or if a third-party library is heavily used in the feature so that a reader can make a more accurate judgement of how much effort went into the feature}

  • Minor enhancement: added a history command that allows the user to navigate to previous commands using up/down keys.

  • Code contributed: [Functional code] [Test code] {give links to collated code files}

  • Other contributions:

    • Project management:

      • Managed releases v1.3 - v1.5rc (3 releases) on GitHub

    • Enhancements to existing features:

      • Updated the GUI color scheme (Pull requests #33, #34)

      • Wrote additional tests for existing features to increase coverage from 88% to 92% (Pull requests #36, #38)

    • Documentation:

      • Did cosmetic tweaks to existing contents of the User Guide: #14

    • Community:

      • PRs reviewed (with non-trivial review comments): #12, #32, #19, #42

      • Contributed to forum discussions (examples: 1, 2, 3, 4)

      • Reported bugs and suggestions for other teams in the class (examples: 1, 2, 3)

      • Some parts of the history feature I added was adopted by several other class mates (1, 2)

    • Tools:

      • Integrated a third party library (Natty) to the project (#42)

      • Integrated a new Github plugin (CircleCI) to the team repo

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Contributions to the User Guide

Given below are sections I contributed to the User Guide. They showcase my ability to write documentation targeting end-users.

Contributions to the Developer Guide

Given below are sections I contributed to the Developer Guide. They showcase my ability to write technical documentation and the technical depth of my contributions to the project.

[Proposed] Undo/Redo feature

Proposed Implementation

The 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.

UndoRedoState0

Step 2. The user executes delete 5 command to delete the 5th person in the address book. The delete command calls Model#commitAddressBook(), causing the modified state of the address book after the delete 5 command executes to be saved in the addressBookStateList, and the currentStatePointer is shifted to the newly inserted address book state.

UndoRedoState1

Step 3. The user executes add n/David …​ to add a new person. The add command also calls Model#commitAddressBook(), causing another modified address book state to be saved into the addressBookStateList.

UndoRedoState2
If a command fails its execution, it will not call Model#commitAddressBook(), so the address book state will not be saved into the addressBookStateList.

Step 4. The user now decides that adding the person 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.

UndoRedoState3
If the currentStatePointer is at index 0, pointing to the initial address book state, then there are no previous address book states to restore. The undo command uses Model#canUndoAddressBook() to check if this is the case. If so, it will return an error to the user rather than attempting to perform the undo.

The following sequence diagram shows how the undo operation works:

UndoSequenceDiagram
The lifeline for UndoCommand should end at the destroy marker (X) but due to a limitation of PlantUML, the lifeline reaches the end of diagram.

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.

If the currentStatePointer is at index addressBookStateList.size() - 1, pointing to the latest address book state, then there are no undone address book states to restore. The redo command uses Model#canRedoAddressBook() to check if this is the case. If so, it will return an error to the user rather than attempting to perform the redo.

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.

UndoRedoState4

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. We designed it this way because it no longer makes sense to redo the add n/David …​ command. This is the behavior that most modern desktop applications follow.

UndoRedoState5

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

CommitActivityDiagram

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 are correct.

Aspect: Data structure to support the undo/redo commands

  • Alternative 1 (current choice): Use a list to store the history of address book states.

    • Pros: Easy for new Computer Science student undergraduates to understand, who are likely to be the new incoming developers of our project.

    • Cons: Logic is duplicated twice. For example, when a new command is executed, we must remember to update both HistoryManager and VersionedAddressBook.

  • Alternative 2: Use HistoryManager for undo/redo

    • Pros: We do not need to maintain a separate list, and just reuse what is already in the codebase.

    • Cons: Requires dealing with commands that have already been undone: We must remember to skip these commands. Violates Single Responsibility Principle and Separation of Concerns as HistoryManager now needs to do two different things.

[Proposed] Data Encryption

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

PROJECT: PowerPointLabs

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