CMPUT 301

Lab 1 Slides

• Lab 1 Slides

CMPUT 301 W26 - Lab 1: Java, OOP, and Android Studio!

1. Setup Instructions

1. Download and install Android Studio from the official Android website.

2. Refer to the installation guide unique to your Operating System.

3. Refer to the lab 1 slides for more information.

2. Walkthrough

The following walkthrough can also be found in this GitHub Repository. Fork this repository for the submission of the Lab exercise.

1. Create a new PetShop project on Android Studio (File > New > New Project > Select "Empty Views Activity").

   [!WARNING] Make sure that the project language is Java, not Kotlin!

2. Create a new Pet class by navigating to File > New > Java Class

3. Add two attributes to the Pet class:

   • String name
   • Date birthDate
   • use Alt + Enter (Windows) or Option + Return (Mac) to import any packages
   • Java coding conventions declares that all attributes are private by default

   [!IMPORTANT] Access modifiers:

   • private : class-only access
   • protected : package and inheritance access
   • public : universal access
   • No modifier : package-level access

4. Create two constructors for the Pet class:

   1. Only name as argument. Use Date = new Date() (current date) for the Default date value.
   2. Both name and birthDate as arguments.

   [!NOTE]

   • All Java classes implicitly extend the Object class (java.lang.Object), which provides basic methods like toString(), equals(), and hashCode() that can be overridden.
   • this refers to the current instance of the class and is used to distinguish between instance variables and constructor parameters.

5. Make a regular Pet in MainActivity by passing in an empty string:

   java Pet pet = new Pet("");

6. Generate getters and setters for the Pet class.

   • Right-click -> Generate -> Getter and Setter -> Shift + Right-click all attributes -> Ok

7. Create a Cat child class that extends the Pet class.

   • Include a super() call in Cat's constructors.
   • Cat inherits Pet's methods and attributes, but requires its own constructors. Try to call super() in the child's constructor:

   java public Cat(String name) { super(name); }

   • super() calls the parent's constructor (there is a hidden call to Object's constructor).

8. Make the Pet Class Abstract

   • Change the Pet class declaration to the following: java public abstract class Pet { ... }

   [!NOTE] Abstract classes cannot be instantiated directly - they can only be used as base classes for inheritance. You must create concrete subclasses to create objects.

   • Change the Pet to a Cat in MainActivity.

   java Cat cat = new Cat("Lucy");

   • Add an abstract method for speaking in the Pet class. It has no implementation and must be overridden by a child classes to add functionality.

   java public abstract String speak();

   [!NOTE] Abstract methods have no implementation and cannot be called directly. They must be overridden by concrete subclasses before they can be used through objects of those subclasses.

9. Method Overriding

   • Cat must override the abstract speak() method from Pet class.
   • The @Override annotation ensures correct method overriding at compile-time.
   • Each child class can implement speak() differently based on its needs.

   java // In Cat class @Override public String speak() { return "meow"; // Cats meow }

10. Make a Dog subclass of Pet

    • call super() in both of Dog's constructors.
    • speak() method should return "bark".
    • What if we want to use both in our list? (hint - implicit upcasting)
    • Add the following to MainActivity:

    ```java Dog dog = new Dog("Snoopy"); ArrayList petList = new ArrayList();

    // Can store both Cat and Dog objects // since they both inherit from Pet petList.add(cat); petList.add(dog); ```

11. Make a Scorpion subclass of Pet

    • call super() in both of Scorpion's constructors.
    • speak() method should return "hiss".
    • What if we want to use both in our list? (hint - implicit upcasting)
    • Add the following to MainActivity:

    java Scorpion scorpion = new Scorpion("Scorponok"); petList.add(scorpion);

12. Interface Implementation

    • Abstract method and base class so all the classes have the speak() method.
    • An interface can also be used to force the use of some methods.

    java public interface Pettable { public Void pet(); }

    • Pet should not implement Pettable because Scorpion should not be pettable
    • Make Cat and Dog classes implement Pettable class.
    • All classes that implement this interface must provide implementations for these methods.

    java ArrayList<Pettable> pettablePets = new ArrayList<Pettable>(); pettablePets.add(cat); pettablePets.add(dog); pettablePets.add(scorpion); // This should produce an error

3. Lab Participation Exercise

1. Add three new model classes to PetShop:
2. An abstract base class which represents the current Mood.
3. Two non-abstract classes which represent different moods (Ex: happy, sad, etc.) and inherit from the abstract class.
4. Each mood should have a date, and getters and setters to access the date.
5. Provide two constructors:
6. One that sets the date to a default
7. One that takes a date as an argument
8. Follow proper encapsulation principles.
9. Each mood should have a method which returns a string representing that mood.
10. Your new code should demonstrate:
11. Classes
12. Methods
13. Attributes
14. Access modifiers
15. Encapsulation
16. Constructors
17. Inheritance
18. Abstract base classes
19. Update the README.md file with your details and references/collaborators.
20. Update the LICENSE.md file with your full name.

[!CAUTION] Make sure to commit and push your code to the GitHub repository before the deadline!

Submission

Submit the repository link to Canvas

Note: Running the project is not necessary.

• Due date: Check the schedule. (Usually Friday after the lab at 5PM)