Question

need help in Java

Now we’ll continue our project by writing a Facebook class that contains an ArrayList of Facebook user objects. The Facebook class should have methods to list all of the users (i.e. print out their usernames), add a user,delete a user, and get the password hint for a user You will also need to create a driver program. The driver should create an instance of the Facebook class and display a menu containing five options: list users add a user, delete a user, get password hint and quit. Then it should read in the user’s choice and call the appropriate method on the Facebook object. This should continue until the user chooses to quit. You don’t need to worry about adding and removing “friends” for this assignment – we’ll do that later in the project.

Here’s the catch: we want the contents of our Facebook object to persist between program executions. To do this, serialize your Facebook object before the program terminates. When the program starts up again, de-serialize the Facebook object rather than creating a new one.

Some details:

When adding a new FacebookUser, prompt the user for the username and check to see that if the users ArrayList already contains a FacebookUser object with that username. If it does, display an error message. If the username is unique, prompt for a password and password hint and create a new FacebookUser object with those values. Add this new user to the users ArrayList.

When deleting a FacebookUser, prompt for the username and check to see that the users ArrayList contains a FacebookUser object with that username. If it doesn’t display an error message. If it does, prompt for the password and check that the FacebookUser object with this username has the same password as the one that was entered. If it doesn’t, display an error message. If the passwords match, delete this FacebookUser object from the users ArrayList.

When retrieving the password hint for a FacebookUser, ask for the username and display an error message if there is no user with that username. Obviously, if the user does exist you should display the password hint without requiring the user’s password.

You will be graded according to the following rubric (each item is worth one point):

The Facebook class has the appropriate fields and methods

The Facebook class can list the FacebookUser objects (i.e. their usernames)

It is possible to add a user at runtime

It is possible to delete a user at runtime

It is possible to get the password hint for a user at runtime

The driver program creates a Facebook object that is serialized before the program ends•

The driver program de-serializes the Facebook object when it starts executing, if a serialized version exists If a serialized version of the Facebook object does not exist, the driver program creates a new Facebook object.

The program compiles

The program runs

The program is clearly written and follows standard coding conventions

Answer 1

//save it as FacebookTest.java

import java.util.Scanner;
import java.util.ArrayList;
import java.io.*;

class FacebookUser implements Serializable{
   String Username;
   String Password;
   String Hint;
  
   FacebookUser(String u, String p, String h){
       Username = u;
       Password = p;
       Hint = h;              
   }  
  
   public String getUsername(){
       return Username;      
   }      
  
   public String getHint(){
       return Hint;      
   }      
  
   public String getPassword(){
       return Password;      
   }
  
}

class Facebook implements Serializable{
   ArrayList<FacebookUser> users;
   static Scanner sc = new Scanner(System.in);
  
   Facebook(){
       users = new ArrayList<FacebookUser>();              
   }
  
   public void listUsers(){
       if (users.size()>0)
       {
           System.out.println("\n---- User list ----- ");      
           for (int i = 0; i < users.size(); i++)
           {
               System.out.println( users.get(i).getUsername() );
           }                      
       }
       else
           System.out.println("No users present in list");          
   }
  
   public void addUser(){
       System.out.print("Enter username:");          
       String user = sc.nextLine();      
      
       //now check if new user is already exists in list
       for (int i = 0; i < users.size(); i++)
           {
               if (users.get(i).getUsername().equals(user))
               {
                   System.out.println( "User already exists..." );                  
                   return;   //if it is already present then return without adding
               }          
           }              
       System.out.print("Enter password:");          
           String pass = sc.nextLine();
       System.out.print("Enter hint:");          
           String hint = sc.nextLine();
          
       FacebookUser u = new FacebookUser(user, pass, hint); // create new user object
       users.add(u);   //add user to list
   }
  
   public void deleteUser(){
       System.out.print("Enter username to delete:");          
       String user = sc.nextLine();      
      
       //now check if user is exists in list
       for (int i = 0; i < users.size(); i++)
           {
               if (users.get(i).getUsername().equals(user)) // if user is found in list
               {                  
                   System.out.print("Enter password:"); //then ask password
                   String pass = sc.nextLine();
                   if ( users.get(i).getPassword().equals(pass) )   //if password matches
                   {
                       users.remove(users.get(i));   //remove user from list
                       System.out.println(user + " Deleted!");
                       return;                                  
                   }
                   else
                   {
                       //otherwise display error message
                       System.out.println("***** Wrong password, cannot delete: " + user);      
                       return;
                   }
               }          
           }                              
       System.out.println("User not found: " + user);          
   }
  
   public void getPassHint(){
       System.out.print("Enter username to get hint: ");
       String user = sc.nextLine();      
      
       //now check if user exists in list
       for (int i = 0; i < users.size(); i++)
           {
               if (users.get(i).getUsername().equals(user)) // if user is found in list
               {
                   System.out.println("Password hint is: " + users.get(i).getHint());                                  
                   return;
               }          
           }                              
       System.out.println("User not found! ");                                  
          
   }
}

public class FacebookTest {
  
   public static void main (String args[]) throws IOException{
      
       Scanner sc = new Scanner(System.in);
       Facebook fb = new Facebook();
      
       //output objects are required for serialization of object
       FileOutputStream fos = null;
       ObjectOutputStream oos = null;      
      
       //input objects are required for de-serialization of object
       FileInputStream fis = null;
       ObjectInputStream ois = null;          
      
       File f = new File("facebookData");   //facebookData is a file to store/serialize Facebook object
      
       if(f.exists()) {   // if file already exists then open it to read data
           fis = new FileInputStream("facebookData");
           ois = new ObjectInputStream(fis);          
           try
           {
               //de-serialize
               fb = (Facebook)ois.readObject();   // read stored object from file and assign to fb object
               //so that fb will contain previously saved data
               System.out.println("Users retrieved: " + fb.users.size());              
           }
           catch (ClassNotFoundException ex)
           {
               System.out.println("Exception during Deserialization: "+ex);              
           }
       }      
      
       fos = new FileOutputStream("facebookData");
       oos = new ObjectOutputStream(fos);              
       fis = new FileInputStream("facebookData");
       ois = new ObjectInputStream(fis);
      
       int choice = 0;
       while(choice!=5)   //if choice is not 5 quit then repeat loop to show menu as follows
       {
           System.out.println("\n----- Facebook -----");
           System.out.println("1. List users");
           System.out.println("2. Add users");
           System.out.println("3. Delete users");
           System.out.println("4. Get Password hint");
           System.out.println("5. Quit");
           System.out.print("Enter your choice: ");
           choice = sc.nextInt();   // get user choice
          
           switch(choice){
               case 1:
                       fb.listUsers();   // list all users
                       break;
               case 2:
                       fb.addUser();   // add user
                       System.out.println("count: " + fb.users.size());
                       break;
               case 3:
                       fb.deleteUser();   // delete user
                       break;
               case 4:
                       fb.getPassHint();   // get password hint for user
                       break;
               case 5:   // quit
                       oos.writeObject(fb); // serialize object data to file (save data to file)
                       oos.flush();   // flush actually writes data to file
                      
                       fos.close();   // close the file stream
                       oos.close();   // close the object stream
                      
                       fis.close();
                       ois.close();
                      
                       break;
               default:
                       System.out.println("*** Invalid choice, try again");
              
           }
          
       }
   }
}

/*   Output

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 1
No users present in list

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 2
Enter username:aa
Enter password:aa
Enter hint:aa
count: 1

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 2
Enter username:bb
Enter password:bb
Enter hint:bb
count: 2

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 3
Enter username to delete:cc
User not found: cc

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 1

---- User list -----
aa
bb

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 2
Enter username:cc
Enter password:cc
Enter hint:cc
count: 3

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 3
Enter username to delete:bb
Enter password:bbb
***** Wrong password, cannot delete: bb

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 3
Enter username to delete:bb
Enter password:bb
bb Deleted!

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 1

---- User list -----
aa
cc

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 4
Enter username to get hint: aa
Password hint is: aa

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 4
Enter username to get hint: bb
User not found!

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 4
Enter username to get hint: cc
Password hint is: cc

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 5

After program restart ------------------

Users retrieved: 2

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice: 1

---- User list -----
aa
cc

----- Facebook -----
1. List users
2. Add users
3. Delete users
4. Get Password hint
5. Quit
Enter your choice:

*/