.

first/restaurant/Address.java

@@ -0,0 +1,16 @@
+package restaurant;
+public class Address {
+    public double latitude , longitude;
+    public String written_address;
+    public double distance_from(Address other) {
+        double xDistance = other.latitude - this.latitude;
+        double yDistance = other.longitude - this.longitude;
+        double distance = Math.sqrt(xDistance * xDistance + yDistance * yDistance);
+        return distance;
+    }    
+    public Address(double latitude, double longitude, String written_address) {
+        this.latitude = latitude;
+        this.longitude = longitude;
+        this.written_address = written_address;
+    }
+}

first/restaurant/Customer.java

@@ -0,0 +1,27 @@
+package restaurant;
+public class Customer {
+    private static int nId = 1;
+    private Address address;
+    private String name;
+    private final int cuNum;
+    public Customer(String name, Address address) {
+        this.cuNum = nId++;
+        this.name = name;
+        this.address = address;
+    }
+    public int getCustomerNumber() {
+        return this.cuNum;
+    }
+    public String getName() {
+        return this.name;
+    }
+    public void setName(String name) {
+        this.name = name;
+    }
+    public Address getAddress() {
+        return this.address;
+    }
+    public void setAddress(Address address) {
+        this.address = address;
+    }
+}

first/restaurant/Food.java

@@ -0,0 +1,21 @@
+package restaurant;
+import java.util.Vector;
+public class Food {
+    private static Vector<Food> menu = new Vector<Food>();
+    private final String name;
+    private final int price;
+    public Food(String name, int price) {
+        this.name = name;
+        this.price = price;
+        menu.add(this);
+    }
+    public String getName() {
+        return this.name;
+    }
+    public int getPrice() {
+        return this.price;
+    }
+    public static Vector<Food> getMenu() {
+        return menu;
+    }
+}

first/restaurant/Invoice.java

@@ -0,0 +1,48 @@
+package restaurant;
+import java.util.ArrayList;
+public class Invoice {
+    private static final float tax_rate = 9.4f;
+    private int state = -1;
+    private Customer customer;
+    private ArrayList<Item> items = new ArrayList<>();
+    public Invoice(String customerName, Address customerAddress) {
+        this.customer = new Customer(customerName, customerAddress);
+    }
+    public Invoice(Customer c1) {
+    }
+    public int getState() {
+        return this.state;
+    }
+    public Customer getCustomer() {
+        return this.customer;
+    }
+    public boolean addItem(Item item) {
+        if (this.state == -1) {
+            this.items.add(item);
+            return true;
+        }
+        return false;
+    }
+    public boolean removeItem(Item item) {
+        if (this.state == -1 && this.items.contains(item)) {
+            this.items.remove(item);
+            return true;
+        }
+        return false;
+    }
+    public void nextStage() {
+        this.state++;
+    }
+    public int getTotalPrice() {
+        double total = 0;
+        for (Item item : this.items) {
+            total += item.getFood().getPrice() * item.getCount();
+        }
+        total += total * tax_rate / 100;
+        return (int) Math.ceil(total);
+    }
+    public ArrayList<Item> getItems() {
+        return this.items;
+    }
+}
+

first/restaurant/Item.java

@@ -0,0 +1,24 @@
+package restaurant;
+public class Item {
+    private final Food food;
+    private final int count;
+    private String description = "";
+    public Item(Food food, int count) {
+        this.food = food;
+        this.count = count;
+    }
+    public Item(Food food, int count , String desc) {
+        this.food = food;
+        this.count = count;
+        this.description = desc;
+    }
+    public Food getFood() {
+        return this.food;
+    }
+    public int getCount() {
+        return this.count;
+    }
+    public String getDescription() {
+        return this.description;
+    }
+}

first/restaurant/Restaurant.java

@@ -0,0 +1,56 @@
+package restaurant;
+public class Restaurant {
+    public static void main(String[] args) {
+        Address a1 = new Address(2, 3, "Lahijan");
+        Address a2 = new Address(5, 6, "Tehran");
+
+        System.out.println("\n--------------------------------------\n");
+        System.out.println("Distance From Address a1 to a2 is: " + a1.distance_from(a2));
+        System.out.println("\n--------------------------------------\n");
+
+        Customer c1 = new Customer("MAMAD", a1);
+        Customer c2 = new Customer("ALI", a2);
+
+        System.out.println("First Customer's ID: " + c1.getCustomerNumber());
+        System.out.println("Second Customer's ID: " + c2.getCustomerNumber());
+
+        Food f1 = new Food("BURGER", 130);
+        Food f2 = new Food("PIZZA", 200);
+        Food f3 = new Food("PASTA", 110);
+
+        System.out.println("\n--------------------------------------\n");
+
+        for (int i = 0; i < Food.getMenu().size(); i++) {
+            System.out.println("Food Name: " + Food.getMenu().get(i).getName());
+        }
+
+        System.out.println("\n--------------------------------------\n");
+
+        Item it1 = new Item(f1, 2);
+        Item it2 = new Item(f2, 3, "MORE SAUCE");
+        Item it3 = new Item(f3, 1);
+
+        Invoice inv = new Invoice(c1);
+
+        if (inv.addItem(it1) && inv.addItem(it2)) System.out.println("Items added successfully");
+        else System.out.println("Items could not be added");
+
+        if (inv.removeItem(it3)) System.out.println("Item removed successfully");
+        else System.out.println("Failed to remove item (item doesn't exist in invoice)");
+
+        inv.nextStage();
+
+        System.out.println("Current state: " + inv.getState());
+
+        System.out.println("\n--------------------------------------\n");
+
+        for (int i = 0; i < inv.getItems().size(); i++) {
+            Item it = inv.getItems().get(i);
+            System.out.println("Food Name: " + it.getFood().getName() + " | Food Description: " + it.getDescription());
+        }
+
+        System.out.println("Total price: " + inv.getTotalPrice());
+    }
+
+
+}