diff --git a/Updated Main to fix issue: Code design and Implementation. b/Updated Main to fix issue: Code design and Implementation.
new file mode 100644
index 0000000..002d8f4
--- /dev/null
+++ b/Updated Main to fix issue: Code design and Implementation.	
@@ -0,0 +1,632 @@
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Scanner;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+
+class Food implements Serializable
+{
+    int itemno;
+    int quantity;  
+    float price;
+   
+    Food(int itemno,int quantity)
+    {
+        this.itemno=itemno;
+        this.quantity=quantity;
+        switch(itemno)
+        {
+            case 1:price=quantity*50;
+                break;
+            case 2:price=quantity*60;
+                break;
+            case 3:price=quantity*70;
+                break;
+            case 4:price=quantity*30;
+                break;
+        }
+    }
+}
+class Singleroom implements Serializable
+{
+    String name;
+    String contact;
+    String gender;  
+    ArrayList<Food> food =new ArrayList<>();
+
+   
+    Singleroom()
+    {
+        this.name="";
+    }
+    Singleroom(String name,String contact,String gender)
+    {
+        this.name=name;
+        this.contact=contact;
+        this.gender=gender;
+    }
+}
+class Doubleroom extends Singleroom implements Serializable
+{
+    String name2;
+    String contact2;
+    String gender2;  
+   
+    Doubleroom()
+    {
+        this.name="";
+        this.name2="";
+    }
+    Doubleroom(String name,String contact,String gender,String name2,String contact2,String gender2)
+    {
+        this.name=name;
+        this.contact=contact;
+        this.gender=gender;
+        this.name2=name2;
+        this.contact2=contact2;
+        this.gender2=gender2;
+    }
+}
+class NotAvailable extends Exception
+{
+    @Override
+    public String toString()
+    {
+        return "Not Available !";
+    }
+}
+
+class holder implements Serializable
+{
+    Doubleroom luxury_doublerrom[]=new Doubleroom[10]; //Luxury
+    Doubleroom deluxe_doublerrom[]=new Doubleroom[20]; //Deluxe
+    Singleroom luxury_singleerrom[]=new Singleroom[10]; //Luxury
+    Singleroom deluxe_singleerrom[]=new Singleroom[20]; //Deluxe
+}
+
+class Hotel
+{
+    static holder hotel_ob=new holder();
+    static Scanner sc = new Scanner(System.in);
+    static List<String> validGender= Arrays.asList("Male","Female","Others");
+    static void CustDetails(int i,int rn) throws Exception
+    {
+        String name, contact, gender;
+        String name2 = null, contact2 = null;
+        String gender2="";
+        System.out.print("\nEnter customer name: ");
+        name = sc.next();
+        System.out.print("Enter contact number: ");
+        contact=sc.next();
+        if(!checkContactNo(contact))
+        {
+            System.out.println("Invalid contact no");
+
+        throw new Exception();
+        }
+        System.out.print("Enter gender: ");
+        gender = sc.next();
+        checkGender(gender);
+
+        if(i<3)
+        {
+        System.out.print("Enter second customer name: ");
+        name2 = sc.next();
+        System.out.print("Enter contact number: ");
+        contact2=sc.next();
+        if(!checkContactNo(contact2))
+        {
+            System.out.println("Invalid contact no");
+
+        throw new Exception();
+        }
+
+        System.out.print("Enter gender: ");
+        gender2 = sc.next();
+        checkGender(gender2);
+
+        }      
+       
+          switch (i) {
+            case 1:hotel_ob.luxury_doublerrom[rn]=new Doubleroom(name,contact,gender,name2,contact2,gender2);
+                break;
+            case 2:hotel_ob.deluxe_doublerrom[rn]=new Doubleroom(name,contact,gender,name2,contact2,gender2);
+                break;
+            case 3:hotel_ob.luxury_singleerrom[rn]=new Singleroom(name,contact,gender);
+                break;
+            case 4:hotel_ob.deluxe_singleerrom[rn]=new Singleroom(name,contact,gender);
+                break;
+            default:System.out.println("Wrong option");
+                break;
+        }
+    }
+   
+    private static boolean checkContactNo(String contact) {
+    Pattern p = Pattern.compile("^\\d{10}$");
+   
+       
+        Matcher m = p.matcher(contact);
+ 
+       
+        return (m.matches()) ;
+}
+
+private static void checkGender(String gender) throws Exception {
+
+    if(!validGender.contains(gender))
+    {
+    System.out.println("Enter valid Gender [Male,Female,Others]");
+    throw new Exception();
+
+
+    }
+}
+
+static void bookroom(int i)
+    {
+        int j;
+        int rn;
+        System.out.println("\nChoose room number from : ");
+        switch (i) {
+            case 1:
+                for(j=0;j<hotel_ob.luxury_doublerrom.length;j++)
+                {
+                    if(hotel_ob.luxury_doublerrom[j]==null)
+                    {
+                        System.out.print(j+1+",");
+                    }
+                }
+                System.out.print("\nEnter room number: ");
+                try{
+                rn=sc.nextInt();
+                rn--;
+                if(hotel_ob.luxury_doublerrom[rn]!=null)
+                    throw new NotAvailable();
+                CustDetails(i,rn);
+                }
+                catch(Exception e)
+                {
+                    System.out.println("Invalid Option");
+                    return;
+                }
+                break;
+            case 2:
+                 for(j=0;j<hotel_ob.deluxe_doublerrom.length;j++)
+                {
+                    if(hotel_ob.deluxe_doublerrom[j]==null)
+                    {
+                        System.out.print(j+11+",");
+                    }
+                }
+                System.out.print("\nEnter room number: ");
+                try{
+                rn=sc.nextInt();
+                rn=rn-11;
+                if(hotel_ob.deluxe_doublerrom[rn]!=null)
+                    throw new NotAvailable();
+                CustDetails(i,rn);
+                }
+                catch(Exception e)
+                {
+                    System.out.println("Invalid Option");
+                    return;
+                }
+                break;
+            case 3:
+                  for(j=0;j<hotel_ob.luxury_singleerrom.length;j++)
+                {
+                    if(hotel_ob.luxury_singleerrom[j]==null)
+                    {
+                        System.out.print(j+31+",");
+                    }
+                }
+                System.out.print("\nEnter room number: ");
+                try{
+                rn=sc.nextInt();
+                rn=rn-31;
+                if(hotel_ob.luxury_singleerrom[rn]!=null)
+                    throw new NotAvailable();
+                CustDetails(i,rn);
+                }
+                catch(Exception e)
+                {
+                    System.out.println("Invalid Option");
+                    return;
+                }
+                break;
+            case 4:
+                  for(j=0;j<hotel_ob.deluxe_singleerrom.length;j++)
+                {
+                    if(hotel_ob.deluxe_singleerrom[j]==null)
+                    {
+                        System.out.print(j+41+",");
+                    }
+                }
+                System.out.print("\nEnter room number: ");
+                try{
+                rn=sc.nextInt();
+                rn=rn-41;
+                if(hotel_ob.deluxe_singleerrom[rn]!=null)
+                    throw new NotAvailable();
+                CustDetails(i,rn);
+                }
+                catch(Exception e)
+                {
+                   System.out.println("Invalid Option");
+                    return;
+                }
+                break;
+            default:
+                System.out.println("Enter valid option");
+                break;
+        }
+        System.out.println("Room Booked");
+    }
+   
+    static void features(int i)
+    {
+        switch (i) {
+            case 1:System.out.println("Number of double beds : 1\nAC : Yes\nFree breakfast : Yes\nCharge per day:4000 ");
+                break;
+            case 2:System.out.println("Number of double beds : 1\nAC : No\nFree breakfast : Yes\nCharge per day:3000  ");
+                break;
+            case 3:System.out.println("Number of single beds : 1\nAC : Yes\nFree breakfast : Yes\nCharge per day:2200  ");
+                break;
+            case 4:System.out.println("Number of single beds : 1\nAC : No\nFree breakfast : Yes\nCharge per day:1200 ");
+                break;
+            default:
+                System.out.println("Enter valid option");
+                break;
+        }
+    }
+   
+    static void availability(int i)
+    {
+      int j,count=0;
+        switch (i) {
+            case 1:
+                for(j=0;j<10;j++)
+                {
+                    if(hotel_ob.luxury_doublerrom[j]==null)
+                        count++;
+                }
+                break;
+            case 2:
+                for(j=0;j<hotel_ob.deluxe_doublerrom.length;j++)
+                {
+                    if(hotel_ob.deluxe_doublerrom[j]==null)
+                        count++;
+                }
+                break;
+            case 3:
+                for(j=0;j<hotel_ob.luxury_singleerrom.length;j++)
+                {
+                    if(hotel_ob.luxury_singleerrom[j]==null)
+                        count++;
+                }
+                break;
+            case 4:
+                for(j=0;j<hotel_ob.deluxe_singleerrom.length;j++)
+                {
+                    if(hotel_ob.deluxe_singleerrom[j]==null)
+                        count++;
+                }
+                break;
+            default:
+                System.out.println("Enter valid option");
+                break;
+        }
+        System.out.println("Number of rooms available : "+count);
+    }
+   
+    static void bill(int rn,int rtype)
+    {
+        double amount=0;
+        String list[]={"Sandwich","Pasta","Noodles","Coke"};
+        System.out.println("\n*******");
+        System.out.println(" Bill:-");
+        System.out.println("*******");
+               
+        switch(rtype)
+        {
+            case 1:
+                amount+=4000;
+                    System.out.println("\nRoom Charge - "+4000);
+                    System.out.println("\n===============");
+                    System.out.println("Food Charges:- ");
+                    System.out.println("===============");
+                     System.out.println("Item   Quantity    Price");
+                    System.out.println("-------------------------");
+                    for(Food obb:hotel_ob.luxury_doublerrom[rn].food)
+                    {
+                        amount+=obb.price;
+                        String format = "%-10s%-10s%-10s%n";
+                        System.out.printf(format,list[obb.itemno-1],obb.quantity,obb.price );
+                    }
+                   
+                break;
+            case 2:amount+=3000;
+                    System.out.println("Room Charge - "+3000);
+                    System.out.println("\nFood Charges:- ");
+                    System.out.println("===============");
+                     System.out.println("Item   Quantity    Price");
+                    System.out.println("-------------------------");
+                    for(Food obb:hotel_ob.deluxe_doublerrom[rn].food)
+                    {
+                        amount+=obb.price;
+                        String format = "%-10s%-10s%-10s%n";
+                        System.out.printf(format,list[obb.itemno-1],obb.quantity,obb.price );
+                    }
+                break;
+            case 3:amount+=2200;
+                    System.out.println("Room Charge - "+2200);
+                    System.out.println("\nFood Charges:- ");
+                    System.out.println("===============");
+                    System.out.println("Item   Quantity    Price");
+                    System.out.println("-------------------------");
+                    for(Food obb:hotel_ob.luxury_singleerrom[rn].food)
+                    {
+                        amount+=obb.price;
+                        String format = "%-10s%-10s%-10s%n";
+                        System.out.printf(format,list[obb.itemno-1],obb.quantity,obb.price );
+                    }
+                break;
+            case 4:amount+=1200;
+                    System.out.println("Room Charge - "+1200);
+                    System.out.println("\nFood Charges:- ");
+                    System.out.println("===============");
+                    System.out.println("Item   Quantity    Price");
+                    System.out.println("-------------------------");
+                    for(Food obb: hotel_ob.deluxe_singleerrom[rn].food)
+                    {
+                        amount+=obb.price;
+                        String format = "%-10s%-10s%-10s%n";
+                        System.out.printf(format,list[obb.itemno-1],obb.quantity,obb.price );
+                    }
+                break;
+            default:
+                System.out.println("Not valid");
+        }
+        System.out.println("\nTotal Amount- "+amount);
+    }
+   
+    static void deallocate(int rn,int rtype)
+    {
+        int j;
+        char w;
+        switch (rtype) {
+            case 1:              
+                if(hotel_ob.luxury_doublerrom[rn]!=null)
+                    System.out.println("Room used by "+hotel_ob.luxury_doublerrom[rn].name);                
+                else
+                {    
+                    System.out.println("Empty Already");
+                        return;
+                }
+                System.out.println("Do you want to checkout ?(y/n)");
+                 w=sc.next().charAt(0);
+                if(w=='y'||w=='Y')
+                {
+                    bill(rn,rtype);
+                    hotel_ob.luxury_doublerrom[rn]=null;
+                    System.out.println("Deallocated succesfully");
+                }
+               
+                break;
+            case 2:
+                if(hotel_ob.deluxe_doublerrom[rn]!=null)
+                    System.out.println("Room used by "+hotel_ob.deluxe_doublerrom[rn].name);                
+                else
+                {    
+                    System.out.println("Empty Already");
+                        return;
+                }
+                System.out.println(" Do you want to checkout ?(y/n)");
+                 w=sc.next().charAt(0);
+                if(w=='y'||w=='Y')
+                {
+                    bill(rn,rtype);
+                    hotel_ob.deluxe_doublerrom[rn]=null;
+                    System.out.println("Deallocated succesfully");
+                }
+                 
+                break;
+            case 3:
+                if(hotel_ob.luxury_singleerrom[rn]!=null)
+                    System.out.println("Room used by "+hotel_ob.luxury_singleerrom[rn].name);                
+                else
+                 {    
+                    System.out.println("Empty Already");
+                        return;
+                }
+                System.out.println(" Do you want to checkout ? (y/n)");
+                w=sc.next().charAt(0);
+                if(w=='y'||w=='Y')
+                {
+                    bill(rn,rtype);
+                    hotel_ob.luxury_singleerrom[rn]=null;
+                    System.out.println("Deallocated succesfully");
+                }
+               
+                break;
+            case 4:
+                if(hotel_ob.deluxe_singleerrom[rn]!=null)
+                    System.out.println("Room used by "+hotel_ob.deluxe_singleerrom[rn].name);                
+                else
+                 {    
+                    System.out.println("Empty Already");
+                        return;
+                }
+                System.out.println(" Do you want to checkout ? (y/n)");
+                 w=sc.next().charAt(0);
+                if(w=='y'||w=='Y')
+                {
+                    bill(rn,rtype);
+                    hotel_ob.deluxe_singleerrom[rn]=null;
+                    System.out.println("Deallocated succesfully");
+                }
+                break;
+            default:
+                System.out.println("\nEnter valid option : ");
+                break;
+        }
+    }
+   
+    static void order(int rn,int rtype)
+    {
+        int i,q;
+        char wish;
+         try{
+             System.out.println("\n==========\n   Menu:  \n==========\n\n1.Sandwich\tRs.50\n2.Pasta\t\tRs.60\n3.Noodles\tRs.70\n4.Coke\t\tRs.30\n");
+        do
+        {
+            i = sc.nextInt();
+            System.out.print("Quantity- ");
+            q=sc.nextInt();
+           
+              switch(rtype){
+            case 1: hotel_ob.luxury_doublerrom[rn].food.add(new Food(i,q));
+                break;
+            case 2: hotel_ob.deluxe_doublerrom[rn].food.add(new Food(i,q));
+                break;
+            case 3: hotel_ob.luxury_singleerrom[rn].food.add(new Food(i,q));
+                break;
+            case 4: hotel_ob.deluxe_singleerrom[rn].food.add(new Food(i,q));
+                break;                                                
+        }
+              System.out.println("Do you want to order anything else ? (y/n)");
+              wish=sc.next().charAt(0);
+        }while(wish=='y'||wish=='Y');  
+        }
+         catch(NullPointerException e)
+            {
+                System.out.println("\nRoom not booked");
+            }
+         catch(Exception e)
+         {
+             System.out.println("Cannot be done");
+         }
+    }
+}
+
+
+class write implements Runnable
+{
+    holder hotel_ob;
+    write(holder hotel_ob)
+    {
+        this.hotel_ob=hotel_ob;
+    }
+    @Override
+    public void run() {
+          try{
+        FileOutputStream fout=new FileOutputStream("backup");
+        ObjectOutputStream oos=new ObjectOutputStream(fout);
+        oos.writeObject(hotel_ob);
+        }
+        catch(Exception e)
+        {
+            System.out.println("Error in writing "+e);
+        }        
+       
+    }
+   
+}
+
+public class Main {
+    public static void main(String[] args){
+       
+        try
+        {          
+        File f = new File("backup");
+        if(f.exists())
+        {
+            FileInputStream fin=new FileInputStream(f);
+            ObjectInputStream ois=new ObjectInputStream(fin);
+            Hotel.hotel_ob=(holder)ois.readObject();
+        }
+        Scanner sc = new Scanner(System.in);
+        int ch,ch2;
+        char wish;
+        x:
+        do{
+
+        System.out.println("\nEnter your choice :\n1.Display room details\n2.Display room availability \n3.Book\n4.Order food\n5.Checkout\n6.Exit\n");
+        ch = sc.nextInt();
+        switch(ch){
+            case 1: System.out.println("\nChoose room type :\n1.Luxury Double Room \n2.Deluxe Double Room \n3.Luxury Single Room \n4.Deluxe Single Room\n");
+                    ch2 = sc.nextInt();
+                    Hotel.features(ch2);
+                break;
+            case 2:System.out.println("\nChoose room type :\n1.Luxury Double Room \n2.Deluxe Double Room \n3.Luxury Single Room\n4.Deluxe Single Room\n");
+                     ch2 = sc.nextInt();
+                     Hotel.availability(ch2);
+                break;
+            case 3:System.out.println("\nChoose room type :\n1.Luxury Double Room \n2.Deluxe Double Room \n3.Luxury Single Room\n4.Deluxe Single Room\n");
+                     ch2 = sc.nextInt();
+                     Hotel.bookroom(ch2);                    
+                break;
+            case 4:
+                 System.out.print("Room Number -");
+                     ch2 = sc.nextInt();
+                     if(ch2>60)
+                         System.out.println("Room doesn't exist");
+                     else if(ch2>40)
+                         Hotel.order(ch2-41,4);
+                     else if(ch2>30)
+                         Hotel.order(ch2-31,3);
+                     else if(ch2>10)
+                         Hotel.order(ch2-11,2);
+                     else if(ch2>0)
+                         Hotel.order(ch2-1,1);
+                     else
+                         System.out.println("Room doesn't exist");
+                     break;
+            case 5:                
+                System.out.print("Room Number -");
+                     ch2 = sc.nextInt();
+                     if(ch2>60)
+                         System.out.println("Room doesn't exist");
+                     else if(ch2>40)
+                         Hotel.deallocate(ch2-41,4);
+                     else if(ch2>30)
+                         Hotel.deallocate(ch2-31,3);
+                     else if(ch2>10)
+                         Hotel.deallocate(ch2-11,2);
+                     else if(ch2>0)
+                         Hotel.deallocate(ch2-1,1);
+                     else
+                         System.out.println("Room doesn't exist");
+                     break;
+            case 6:break x;
+               
+        }
+           
+            System.out.println("\nContinue : (y/n)");
+            wish=sc.next().charAt(0);
+            if(!(wish=='y'||wish=='Y'||wish=='n'||wish=='N'))
+            {
+                System.out.println("Invalid Option");
+                System.out.println("\nContinue : (y/n)");
+                wish=sc.next().charAt(0);
+            }
+           
+        }while(wish=='y'||wish=='Y');    
+       
+        Thread t=new Thread(new write(Hotel.hotel_ob));
+        t.start();
+        }        
+            catch(Exception e)
+            {
+                System.out.println("Not a valid input");
+            }
+    }
+}