HW1 - Eric Tran

homework/src/HW1/submissions/partA/erictran/airbnb/BookingService.java

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+package HW1.submissions.partA.erictran.airbnb;
+
+public interface BookingService {
+    int calculateTotalPrice(Hotel hotel, int numberOfNights);
+}

homework/src/HW1/submissions/partA/erictran/airbnb/BookingServiceImpl.java

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+package HW1.submissions.partA.erictran.airbnb;
+
+public class BookingServiceImpl implements BookingService {
+    @Override
+    public int calculateTotalPrice(Hotel hotel, int numberOfNights) {
+        int totalPrice = hotel.calculateTotalPrice(numberOfNights);
+        if (hotel instanceof DiscountedHotel) {
+            totalPrice -= 50;
+        }
+        return totalPrice;
+    }
+}

homework/src/HW1/submissions/partA/erictran/airbnb/DiscountedHotel.java

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+package HW1.submissions.partA.erictran.airbnb;
+
+public class DiscountedHotel extends Hotel {
+}

homework/src/HW1/submissions/partA/erictran/airbnb/ExtraFeesService.java

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+package HW1.submissions.partA.erictran.airbnb;
+
+public interface ExtraFeesService {
+    int calculateExtraGuestsFees(Hotel hotel, int numberOfGuests);
+}

homework/src/HW1/submissions/partA/erictran/airbnb/ExtraFeesServiceImpl.java

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+package HW1.submissions.partA.erictran.airbnb;
+
+public class ExtraFeesServiceImpl implements ExtraFeesService{
+    @Override
+    public int calculateExtraGuestsFees(Hotel hotel, int numberOfGuests) {
+        return hotel.calculateExtraGuestsFees(numberOfGuests);
+    }
+}

homework/src/HW1/submissions/partA/erictran/airbnb/Hotel.java

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+package HW1.submissions.partA.erictran.airbnb;
+
+public class Hotel {
+    int calculateTotalPrice(int numberOfNights) {
+        return numberOfNights * 100;
+    }
+
+    int calculateExtraGuestsFees(int numberOfGuests) {
+        if (numberOfGuests > 6) {
+            return (numberOfGuests - 6) * 30;
+        }
+        return 0;
+    }
+}

homework/src/HW1/submissions/partA/erictran/airbnb/Main.java

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+package HW1.submissions.partA.erictran.airbnb;
+
+public class Main {
+    public static void main(String[] args) {
+        Hotel regularHotel = new Hotel();
+        DiscountedHotel discountedHotel = new DiscountedHotel();
+
+        BookingService bookingService = new BookingServiceImpl();
+        ExtraFeesService extraFeesService = new ExtraFeesServiceImpl();
+        int regularHotelTotalPrice = bookingService.calculateTotalPrice(regularHotel, 3);
+        int discountedHotelTotalPrice = bookingService.calculateTotalPrice(discountedHotel, 3);
+        int regularHotelExtraGuestsFees = extraFeesService.calculateExtraGuestsFees(regularHotel, 7);
+        int discountedHotelExtraGuestsFees = extraFeesService.calculateExtraGuestsFees(discountedHotel, 8);
+
+        System.out.println("Regular Hotel Total Price: $" + regularHotelTotalPrice);
+        System.out.println("Discounted Hotel Total Price: $" + discountedHotelTotalPrice);
+        System.out.println("Regular Hotel Extra Guests Fees: $" + regularHotelExtraGuestsFees);
+        System.out.println("Discounted Hotel Extra Guests Fees: $" + discountedHotelExtraGuestsFees);
+    }
+}

homework/src/HW1/submissions/partA/erictran/airbnb/README.md

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+# 'Airbnb' Violation of SOLID
+
+This code violates the "L" in SOLID, which stands for Liskov Substitution Principle
+<br />
+<br />
+It officially states that "Objects of a superclass shall be replaceable with objects of its subclasses without breaking the application."
+In other words, if you have a reference to a base type object, you should be able to use it to refer to a subtype object without any issues.
+In this case, the 'DiscountedHotel' class changes the behavior of the 'calculateTotalPrice()' method.
+Consider how the 'calculateTotalPrice' method in the 'Hotel' class returns the number of nights multiplied by the nightly rate while in the 'DiscountedHotel' class
+it returns the total price minus a discount.
+<br />
+<br />
+Hence, we cannot substitute a 'DiscountedHotel' object for a 'Hotel' object without breaking the code.
+For example, if we passed a 'DiscountedHotel' object to the bookService.calculateTotalPrice() method, the total price may be calculated incorrectly.
+<br />
+<br />
+A better design approach for this is to move the discount logic to the 'BookingServiceImpl' class.
+<br />
+<br />
+Lets start off by removing the 'calculateTotalPrice' method from the 'DiscountedHotel' class:
+```
+public class DiscountedHotel extends Hotel {
+
+}
+```
+Now, lets refactor the 'calculateTotalPrice' in the 'BookingServiceImpl' class so that it checks if the current instance is a 'DiscountedHotel' object before applying the discount.
+```
+public class BookingServiceImpl implements BookingService {
+    @Override
+    public int calculateTotalPrice(Hotel hotel, int numberOfNights) {
+        int totalPrice = hotel.calculateTotalPrice(numberOfNights);
+        if (hotel instanceof DiscountedHotel) {
+            totalPrice -= 50;
+        }
+        return totalPrice;
+    }
+}
+```
+After making the following changes, the code now adheres to the Liskov Substitution Principle of SOLID.
+<br />
+<br />
+We have a Main class to test the new code. It should produce the following output:
+```
+Regular Hotel Total Price: $300
+Discounted Hotel Total Price: $250
+```

homework/src/HW1/submissions/partA/erictran/doordash/Customer.java

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+package HW1.submissions.partA.erictran.doordash;
+
+public class Customer {
+    private String name;
+
+    public Customer(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+}

homework/src/HW1/submissions/partA/erictran/doordash/DeliveryService.java

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+package HW1.submissions.partA.erictran.doordash;
+
+public interface DeliveryService {
+    void deliverFood(Restaurant restaurant, Customer customer);
+}

homework/src/HW1/submissions/partA/erictran/doordash/FoodDeliveryService.java

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+package HW1.submissions.partA.erictran.doordash;
+
+public class FoodDeliveryService implements DeliveryService {
+    @Override
+    public void deliverFood(Restaurant restaurant, Customer customer) {
+        System.out.println("Food delivered from " + restaurant.getName() + " to " + customer.getName());
+    }
+}

homework/src/HW1/submissions/partA/erictran/doordash/Main.java

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+package HW1.submissions.partA.erictran.doordash;
+
+public class Main {
+    public static void main(String[] args) {
+        Restaurant restaurant = new Restaurant("Chick-fil-a");
+        Customer customer = new Customer("Bobby");
+
+        DeliveryService deliveryService = new FoodDeliveryService();
+        PackageTrackingService trackingService = new PackageTrackingService();
+
+        deliveryService.deliverFood(restaurant, customer);
+
+        trackingService.trackPackage("123456789");
+
+        trackingService.calculateEstimatedDeliveryTime(100, 55);
+    }
+}

homework/src/HW1/submissions/partA/erictran/doordash/PackageTrackingService.java

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+package HW1.submissions.partA.erictran.doordash;
+
+public class PackageTrackingService implements TrackingService {
+    @Override
+    public void trackPackage(String trackingNumber) {
+        System.out.println("Package with tracking number " + trackingNumber + " is being tracked.");
+    }
+
+    @Override
+    public void calculateEstimatedDeliveryTime(double distanceInMiles, double deliverySpeedMPH) {
+        double estimatedDeliveryTime = distanceInMiles / deliverySpeedMPH;
+        System.out.printf("Package will be delivered in approximately %.2f hours.\n", estimatedDeliveryTime);
+    }
+}

homework/src/HW1/submissions/partA/erictran/doordash/README.md

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+# 'DoorDash' Violation of SOLID
+
+This code violates the "I" in SOLID, which stands for Interface Segregation Principle.
+<br />
+<br />
+It officially states that "Clients should not be forced to depend on methods they do not use."
+Examining the "FoodDeliveryAndTrackingService" class, it has two responsibilities, one
+being delivering food and the other being tracking packages.
+Though, clients that only need to deliver food do not need to depend on the trackPackage() method.
+<br />
+<br />
+A better design approach is to split the "FoodDeliveryAndTrackingService" class into two.
+For example, we can split the code into "FoodDeliveryService" and "PackageTrackingService."
+<br />
+<br />
+We need to alter 'DeliveryService' interface so that it focuses on Food Delivery only:
+```
+package doordash;
+
+public interface DeliveryService {
+    void deliverFood(Restaurant restaurant, Customer customer);
+}
+```
+We create a new 'FoodDeliveryService' class that focuses on Food Delivery only:
+```
+package doordash;
+
+public class FoodDeliveryService implements DeliveryService {
+    @Override
+    public void deliverFood(Restaurant restaurant, Customer customer) {
+        System.out.println("Food delivered from " + restaurant.getName() + " to " + customer.getName());
+    }
+}
+```
+We create a new 'TrackingService' interface so that it focuses on Package Tracking only:
+```
+package doordash;
+
+public interface TrackingService {
+    void trackPackage(String trackingNumber);
+}
+```
+We create a new 'PackageTrackingService' class that focuses on Package Tracking only:
+```
+package doordash;
+
+public class PackageTrackingService implements TrackingService {
+    @Override
+    public void trackPackage(String trackingNumber) {
+        System.out.println("Package with tracking number " + trackingNumber + " is being tracked.");
+    }
+}
+```
+After making the following changes, the code now adheres to the Interface Segregation Principle.
+of SOLID.
+<br />
+<br />
+We have a Main class to test the new code. It should produce the following output:
+```
+Food delivered from Chick-fil-a to Bobby
+Package with tracking number 123456789 is being tracked.
+```

homework/src/HW1/submissions/partA/erictran/doordash/Restaurant.java

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+package HW1.submissions.partA.erictran.doordash;
+
+public class Restaurant {
+    private String name;
+
+    public Restaurant(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+}

homework/src/HW1/submissions/partA/erictran/doordash/TrackingService.java

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+package HW1.submissions.partA.erictran.doordash;
+
+public interface TrackingService {
+    void trackPackage(String trackingNumber);
+
+    void calculateEstimatedDeliveryTime(double distanceInMiles, double deliverySpeedMPH);
+}

homework/src/HW1/submissions/partA/erictran/facebook/ImagePost.java

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+package HW1.submissions.partA.erictran.facebook;
+
+public class ImagePost extends Post {
+    private String imageUrl;
+
+    public ImagePost(String text, String imageUrl) {
+        super(text);
+        this.imageUrl = imageUrl;
+    }
+
+    public String getImageUrl() {
+        return imageUrl;
+    }
+
+    public void setImageUrl(String imageUrl) {
+        this.imageUrl = imageUrl;
+    }
+
+    @Override
+    public void display() {
+        System.out.print("Image post: ");
+        System.out.println(imageUrl);
+    }
+}

homework/src/HW1/submissions/partA/erictran/facebook/LiveVideoPost.java

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+package HW1.submissions.partA.erictran.facebook;
+
+public class LiveVideoPost extends Post {
+    private String liveVideoUrl;
+
+    public LiveVideoPost(String text, String liveVideoUrl) {
+        super(text);
+        this.liveVideoUrl = liveVideoUrl;
+    }
+
+    public String getLiveVideoUrl() {
+        return liveVideoUrl;
+    }
+
+    public void setLiveVideoUrl(String videoUrl) {
+        this.liveVideoUrl = videoUrl;
+    }
+
+    @Override
+    public void display() {
+        System.out.print("Video post: ");
+        System.out.println(liveVideoUrl);
+    }
+}

homework/src/HW1/submissions/partA/erictran/facebook/Main.java

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+package HW1.submissions.partA.erictran.facebook;
+
+public class Main {
+    public static void main(String[] args) {
+        TextPost textPost = new TextPost("This is a text post.");
+        ImagePost imagePost = new ImagePost("Check out this image!", "https://example.com/image.jpg");
+        VideoPost videoPost = new VideoPost("Watch this video!", "https://example.com/video.mp4");
+        LiveVideoPost liveVideoPost = new LiveVideoPost("Join my stream!", "rtmp://facebook.com/live");
+
+        System.out.println("Text Post Test:");
+        textPost.display();
+        System.out.println("\nImage Post Test:");
+        imagePost.display();
+        System.out.println("\nVideo Post Test:");
+        videoPost.display();
+        System.out.println("\nLive Video Post Test:");
+        liveVideoPost.display();
+
+        textPost.setText("Updated text post.");
+        System.out.println("\nUpdated Text Post:");
+        textPost.display();
+        imagePost.setImageUrl("https://example.com/image2.jpg");
+        System.out.println("\nUpdated Image Post:");
+        imagePost.display();
+        videoPost.setVideoUrl("https://example.com/video2.mp4");
+        System.out.println("\nUpdated Video Post:");
+        videoPost.display();
+        liveVideoPost.setLiveVideoUrl("rtmp://facebook.com/live2");
+        System.out.println("\nUpdated Live Video Post:");
+        liveVideoPost.display();
+    }
+}

homework/src/HW1/submissions/partA/erictran/facebook/Post.java

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+package HW1.submissions.partA.erictran.facebook;
+
+abstract class Post {
+    protected String text;
+
+    public Post(String text) {
+        this.text = text;
+    }
+
+    public void setText(String text) {
+        this.text = text;
+    }
+
+    public String getText() {
+        return text;
+    }
+
+    public void display() {
+        System.out.println(text);
+    }
+}