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Learning Outcomes

After studying this code and completing the corresponding exercises, you should be able to,

  1. Utilize User Stories [LO-UserStories]
  2. Utilize use cases [LO-UseCases]
  3. Use Non Functional Requirements [LO-NFR]
  4. Use Polymorphism [LO-Polymorphism]
  5. Use abstract classes/methods [LO-Abstract]
  6. Follow Liskov Substitution Principle [LO-LSP]
  7. Use Java-FX for GUI programming [LO-JavaFx]
  8. Analyze Coupling and Cohesion of designs [LO-CouplingCohesion]
  9. Apply Dependency Inversion Principle [LO-DIP]
  10. Use Dependency Injection [LO-DI]
  11. Apply Open-Closed Principle [LO-OCP]
  12. Work in a 2KLoC code base [LO-2KLoC]

Utilize User Stories [LO-UserStories]

Exercise: Add more user stories

  • Assume you are planing to expand the functionality of the AddressBook (but keep it as a CLI application). What other user stories do you think AddressBook should support? Add those user stories to the DeveloperGuide.md.

Utilize use cases [LO-UseCases]

Exercise: Add a 'Rename tag' use case

  • Add a use case to the DeveloperGuide.md to cover the case of renaming of an existing tag.
    e.g. rename the tag friends to buddies (i.e. all persons who had the friends tag will now have a buddies tag instead)
    Assume that AddressBook confirms the change with the user before carrying out the operation.

Use Non Functional Requirements [LO-NFR]

Exercise: Add more NFRs

  • Add some more NFRs to the DeveloperGuide.md

Use Polymorphism [LO-Polymorphism]

Note how the Command::execute() method shows polymorphic behavior.

Exercise: Add a polymorphic isMutating method

  • Add an abstract method boolean isMutating() to the Command class. This method will return true for command types that mutate the data. e.g. AddCommand
  • Currently, AddressBook data are saved to the file after every command. Take advantage of the the new method you added to limit file saving to only for command types that mutate data.
    i.e. add command should always save the data while list command should never save data to the file.

Note: There may be better ways to limit file saving to commands that mutate data. The above approach, while not optimal, will give you chance to implement a polymorphic behavior.

Use abstract classes/methods [LO-Abstract]

Covered by [LO-Polymorphism]

Follow Liskov Substitution Principle [LO-LSP]

Exercise: Add an exception to an overridden method

  • Add a throws Exception clause to the AddCommand::execute method. Notice how Java compiler will not allow it, unless you add the same throws clause to the parent class method. This is because if a child class throws an exception that is not specified by the Parent's contract, the child class is no longer substitutable in place of the parent class.
  • Also note that while in the above example the compiler enforces LSP, there are other situations where it is up to the programmer to enforce it. For example, if the method in the parent class works for null input, the overridden method in the child class should not reject null inputs. This will not be enforced by the compiler.

Use Java-FX for GUI programming [LO-JavaFx]

Resources

Exercise: Add class-level members

  • If you are new to JavaFX, follow our tutorial given above.
  • Do some enhancements to the AddressBook GUI. e.g. add an application icon, change size/style

Analyze Coupling and Cohesion of designs [LO-CouplingCohesion]

  • Ensure you know the answers to these questions:
    • What is the Coupling?
    • What is Cohesion?
  • As you saw above, DIP helps us to avoid coupling from higher-level classes to lower-level classes.
  • Notice how having a separate Formattter class (an application of SIP) improves the cohesion of the MainWindow class as well as the Formatter class.

Exercise: Identify places to reduce coupling and increase cohesion

  • Where else in the design coupling can be reduced further, or cohesion can be increased further?

Apply Dependency Inversion Principle [LO-DIP]

Exercise: Invert dependency from Logic to Storage

  • Ensure you know the answers to these questions:
    • What is the Dependency Inversion Principle?
    • How does DIP help?
  • Note how Logic class depends on the StorageFile class. This is a violation of DIP.
  • Modify the implementation as follows so that both Logic and StorageFile now depend on the abstract class Storage.
  • Where else in the code do you notice the application of DIP?

Use Dependency Injection [LO-DI]

Note how Logic class depends on the StorageFile class. This means when testing the Logic class, our test cases execute the StorageFile class as well. What if we want to test the Logic class without getting the StorageFile class involved? That is a situation where we can use Dependency Injection.

Exercise: Facilitate injecting a StorageStub

  • Ensure you know the answers to these questions:

    • What is the Dependency Injection?
    • How does DI help?

  • Change the implementation as follows so that we can inject a StorageStub when testing the Logic class.

    If you did the exercise in LO-DIP already but those changes are in a different branch, you may be able to reuse some of those commits by cherry picking them from that branch to the branch you created for this exercise.
    Note: cherry picking is simply copy-pasting a commit from one branch to another. In SourceTree, you can right-click on the commit your want to copy to the current branch, and choose 'Cherry pick'

  • Implement the StorageStub such that calls to the save method do nothing (i.e. empty method body).

  • Update the LogicTest to work with the StorageStub instead of the actual StorageFile object.
    i.e. Logic injects a StorageStub object to replace the dependency of Logic on StorageFile before testing Logic.

  • The example above uses DIP as a means to achieve DI. Note that there is another way to inject a StorageStub object, as shown below. In this case we do not apply the DIP but we still achieve DI.

Apply Open-Closed Principle [LO-OCP]

Exercise: Analyze OCP-compliance of the Logic class

  • Ensure you know the answers to these questions:
    • What is the Open Closed Principle?
    • How does OCP help?
  • Consider adding a new command to the Address Book. e.g. an edit command.
  • Notice how little you need to change in the Logic class to extend its behavior so that it can execute the new command. That is because Logic follows the OCP i.e. Logic is open to be extended with more commands but closed for modifications.
  • Is it possible to make the Parser class more OCP-compliant in terms of extending it to handle more command types?
  • In terms of how it saves data, does Logic become more OCP-compliant after applying DIP as given in LO-DIP? How can you improve Logic's OCP-compliance further so that it can not only work with different types of storages, but different number of storages (e.g. save to both a text file and a database).

Work in a 2KLoC code base [LO-2KLoC]

Exercise: Enhance AddressBook

  • Enhance AddressBook in some way. e.g. add a new command