HW1 Submission by Edward

CS151.iml

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+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/homework/src" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>

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

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-Add your submissions for part A of the homework here. 
+Edward's submission for HW1 Part A

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

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

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

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+package HW1.submissions.partA.airbnb;
+
+public class BookingServiceImpl implements BookingService{
+    @Override
+    public int calculateTotalPrice(HotelInterface hotel, int numberOfNights){
+        int totalPrice = hotel.calculateTotalPrice(numberOfNights);
+        return totalPrice;
+    }
+}

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

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+package HW1.submissions.partA.airbnb;
+
+public class DiscountedHotel implements HotelInterface{
+    @Override
+    public int calculateTotalPrice(int numberOfNights){
+        return numberOfNights*50;
+    }
+}

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

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+package HW1.submissions.partA.airbnb;
+
+public class Hotel implements HotelInterface{
+    @Override
+    public int calculateTotalPrice(int numberOfNights){
+        return numberOfNights*100;
+    }
+}

homework/src/HW1/submissions/partA/airbnb/HotelInterface.java

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+package HW1.submissions.partA.airbnb;
+
+public interface HotelInterface {
+    int calculateTotalPrice(int numberOfNights);
+}

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

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+package HW1.submissions.partA.airbnb;
+
+public class Main {
+    public static void main(String[] args){
+        HotelInterface regularHotel = new Hotel();
+        HotelInterface discountedHotel = new DiscountedHotel();
+
+        BookingService bookingService = new BookingServiceImpl();
+        int regularHotelTotalPrice = bookingService.calculateTotalPrice(regularHotel, 3);
+        int discountedHotelTotalPrice = bookingService.calculateTotalPrice(discountedHotel, 3);
+
+        System.out.println("Regular Hotel Total Price: $"+regularHotelTotalPrice);
+        System.out.println("Discounted Hotel Total Price: $"+discountedHotelTotalPrice);
+    }
+}

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

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+Q) which SOLID principle(s) is this company violating?  
+A) this company violates Liskov Substitution Principle and Open Closed Principle.  
+
+Q) Your approach to making changes to fix the violation  
+A) LSP is satisfied by introducing an interface HotelInterface which is implemented by the class Hotel and the class DiscountedHotel.
+Consequently, in the interface BookingService and the class BookingServiceImpl, the method calculateTotalPrice takes a parameter of type HotelInterface rather than type Hotel.
+OCP is satisfied as further additions of hotels/ specific hotel features can now be done without modifying existing classes or class contents but rather just extending them.

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

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

homework/src/HW1/submissions/partA/doordash/Deliverable.java

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+package HW1.submissions.partA.doordash;
+
+public interface Deliverable {
+    void deliverPackage(Seller seller, Customer customer);
+}

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

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+package HW1.submissions.partA.doordash;
+
+public class FoodDeliveryService implements Deliverable{
+    @Override
+    public void deliverPackage(Seller seller, Customer customer) {
+        if(seller instanceof Restaurant that) {
+            System.out.println("Food delivered from " + that.getName() + " to " + customer.getName());
+        }
+        else{
+            System.out.println("We support only restaurant orders for now!");
+        }
+    }
+}

homework/src/HW1/submissions/partA/doordash/FoodTrackingService.java

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+package HW1.submissions.partA.doordash;
+
+public class FoodTrackingService implements Trackable{
+    @Override
+    public void trackPackage(String trackingNumber) {
+        System.out.println("Package with tracking number " + trackingNumber + "is being tracked.");
+    }
+}

homework/src/HW1/submissions/partA/doordash/GroceryStore.java

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

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

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+package HW1.submissions.partA.doordash;
+
+public class Main {
+    public static void main(String[] args){
+        FoodDeliveryService foodDeliveryService = new FoodDeliveryService();
+        FoodTrackingService foodTrackingService = new FoodTrackingService();
+
+        foodDeliveryService.deliverPackage(new Restaurant("McDonalds"), new Customer("Anant"));
+        foodDeliveryService.deliverPackage(new GroceryStore("Safeway"), new Customer("Edward"));
+        foodTrackingService.trackPackage("5E96MQ3XPL");
+    }
+}

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

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+1) which SOLID principle(s) is this company violating?  
+This company violates Single Responsibility Principle and Interface Segregation Principle.
+
+
+2) Your approach to making changes to fix the violation
+ISP is satisfied by breaking down the interface DeliveryService into more client-specific interfaces Deliverable and Trackable.
+Consequently, the class FoodDeliveryAndTrackingService is also broken down into class FoodDeliveryService and class FoodTrackingService
+with each correspondingly implementing Deliverable interface and Trackable interface, thus making SRP satisfied. While not violating yet, based on the recent
+capabilities, using Restaurant class my potentially violate LSP since items beyond food can be ordered on DoorDash, so I created an interface Seller
+with the class Restaurant implementing it for future expansions. I also made use of instanceof operator and 'that' keyword to verify 
+this recent version supports only the restaurant orders for now.

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

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

homework/src/HW1/submissions/partA/doordash/Seller.java

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+package HW1.submissions.partA.doordash;
+
+public interface Seller {
+
+}

homework/src/HW1/submissions/partA/doordash/Trackable.java

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+package HW1.submissions.partA.doordash;
+
+public interface Trackable {
+    void trackPackage(String trackingNumber);
+}

homework/src/HW1/submissions/partA/facebook/Image.java

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+package HW1.submissions.partA.facebook;
+
+public class Image {
+    private String imageUrl;
+    private boolean isImage;
+
+    public Image(String imageUrl){
+        this.imageUrl = imageUrl;
+        this.isImage = true;
+    }
+    public String getImageUrl(){return imageUrl;}
+    public boolean isImage(){return isImage;}
+}

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

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+package HW1.submissions.partA.facebook;
+
+public class Main {
+    public static void main(String[] args){
+        Post post1 = new Post(new Text("text-only post"));
+        Post post2 = new Post(new Text("text and image post"), new Image("...some image url..."));
+        Post post3 = new Post(new Text("text and video post"), new Video("...some video url..."));
+        Post post4 = new Post(new Text("text, image, and video post"), new Image("...some image url..."), new Video("...some video url..."));
+
+        System.out.println(post1);
+        System.out.println(post2);
+        System.out.println(post3);
+        System.out.println(post4);
+    }
+}

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

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+package HW1.submissions.partA.facebook;
+
+public class Post {
+    private Text text;
+    private Image image;
+    private Video video;
+
+    public Post(Text text){
+        this.text = text;
+    }
+    public Post(Text text, Image image){
+        this.text = text;
+        this.image = image;
+    }
+    public Post(Text text, Video video){
+        this.text = text;
+        this.video = video;
+    }
+    public Post(Text text, Image image, Video video){
+        this.text = text;
+        this.image = image;
+        this.video = video;
+    }
+
+    public void displayText(){
+        System.out.println(text.getText());
+    }
+
+    @Override
+    public String toString(){
+        return "Post: " + text.getText() + "\n" +
+               "Image: " + (image != null ? image.getImageUrl() : "NO image url provided") + "\n" +
+               "Video: " + (video != null ? video.getVideoUrl() : "NO video url provided") + "\n";
+    }
+}

homework/src/HW1/submissions/partA/facebook/README.md

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+1) which SOLID principle(s) is this company violating?
+This company violates Single Responsibility Principle.
+
+2) Your approach to making changes to fix the violations.
+Post2 class violates SRP because it looks 'fat' with multiple sets of related attributes.
+Once implemented with methods, such class layout can easily get swamped with multiple methods that function differently on various not-so-related attributes.
+I split the class Post2 into classes - Post, Text, Image and Video - each of which can be configured with more specific attributes and methods for further development while also allowing each to either extend a superclass or implement interfaces to provide more enriched features.

homework/src/HW1/submissions/partA/facebook/Text.java

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+package HW1.submissions.partA.facebook;
+
+public class Text {
+    private String text;
+
+    public Text(String text){this.text = text;}
+    public String getText(){return text;}
+}

homework/src/HW1/submissions/partA/facebook/Video.java

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+package HW1.submissions.partA.facebook;
+
+public class Video {
+    private String videoUrl;
+    private boolean isVideo;
+
+    public Video(String videoUrl){
+        this.videoUrl = videoUrl;
+        this.isVideo = true;
+    }
+    public String getVideoUrl(){return videoUrl;}
+    public boolean isVideo(){return isVideo;}
+}

homework/src/HW1/submissions/partA/paypal/Account.java

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+package HW1.submissions.partA.paypal;
+
+public class Account {
+    private String accountID;
+
+    public Account(String accountID){
+        this.accountID = accountID;
+    }
+
+    public String getAccountID(){return accountID;}
+}

homework/src/HW1/submissions/partA/paypal/Main.java

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+package HW1.submissions.partA.paypal;
+
+public class Main {
+    public static void main(String[] args){
+        PayEntity payEntity = new PayEntity();
+
+        payEntity.setPaymentProcessorService(new PaymentProcessor(new Account("123456789")));
+        payEntity.process(150);
+
+        payEntity.setPaymentProcessorService(new PayPalGateway(new Account("987654321")));
+        payEntity.process(300);
+
+        payEntity.setPaymentProcessorService(null);
+        payEntity.process(500);
+    }
+}