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Lab #6.md

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Programming 2 - Lab #6 : Encapsulation

By TA Ahmed Arafat (Ahmed Mohamed Yousry)

Topics To Be Discussed:

  1. Encapsulation
    1. Access Modifiers for Attributes/Method (public/private/protected/default)
    2. Access Modifiers for classes (public/default)
    3. Package & SubPackage
    4. Getter & Setter
    5. Types Of Packages (Built-in/User-defined)
  2. this Operator
  3. Solving 3 OOP Programs
  1. Encapsulation: mean that all important information is contained inside an object. (Data security)
  • Practicing Time :
import java.util.Scanner;
import SocialMedia.*;

public class Account {
        // getter & setter methods
    //null // false // 0
    private String username;// ahmed
    public String Password;
    private double Balance;// -1
    Account(String u)
    {
        Balance = 0;
        username = u;
    }

    public double getBalance()
    {
       // return this.Balance - (this.Balance * 0.1);// 100 - 10 = 90
        return this.Balance ;
    }

    public String getUsername()
    {
        return username + "@facebook.com";///1234
    }
    public void setBalance(int b)
    {
            if(b < 0)
            {
                System.out.println("Please Enter a balance greater than or equal to zero");
                return;
            }
            this.Balance = b;
    }
}


class Lab6 {
    public static void main(String[] args) {
        Account obj = new Account("ahmed");
            //  username -> ahmed @facebook.com
       System.out.println(obj.getBalance());
       System.out.println(obj.getUsername());
            obj.setBalance(100);
        System.out.println(obj.getBalance());

    }
}

Problem #1 :

  • Create a class called BankSystem.BankAcc in a package called BankSystem,
  • With properties name-age-email-password-balance
  • Each of name-age are accessible everywhere while email is only accessible inside that package,
  • While password-balance are accessible only inside that class
  • Then create an initialization method that is called automatically when an object is created from that class that initialize both name-age-balance with any value from the user (take an input from him)
  • Then in this initialization method call a setter() method that set the value of email attribute, this method checks if the email contains @ & . characters then if the email does not contain one of them it still takes input from the user till the email contains both of them
  • Then create another setter method that set the password attribute,
  • This method takes the password from the user and then store it encrypted (using Caesar cipher)
  • All of the above methods are called inside the constructor (Remember)
  • Then inside that class, create 2 getter() methods that just print value of email and encrypted password
  • Finally, create a LogIn(email,password) method that takes an email & password from the user then check if they are matched with values in that object or not
  • If yes then print text "welcome back" + Name of that user Otherwise print "Not Authorized, Please Try Again"
  • Finally print the number of created Accounts from that class (Hint: use static attribute to count number of created objects)

Solution

  • BackAcc.java file
package BankSystem;

import java.util.Scanner;

public class BankAcc {
    static int NumOfAcc = 0;
    // attributes of our class BankAcc
    public String name;
    String email; // [email protected]
    private String password;// cb
    public int age;
    private double balance;

    // Parametrized Constructor for class BankAcc
    public BankAcc(String name, int age, double balance, String Password) {
        this.name = name;
        this.age = age;
        this.balance = balance;
        setPassword(Password);
        setEmail();
        NumOfAcc++;
    }

    private boolean IsEmailValid(String em) {
        int cnt_at = 0, cnt_dot = 0;//[email protected]
        for (int i = 0; i < em.length(); i++) {
            if (em.charAt(i) == '@') cnt_at++;
            if (em.charAt(i) == '.') cnt_dot++;
        }
        if (cnt_at == 1 && cnt_dot == 1) return true;
        return false;
    }

    public void setEmail()// @ .
    {
        System.out.println("please enter a valid email");
        Scanner sc = new Scanner(System.in);
        String temp_email = sc.next();
        while (!IsEmailValid(temp_email)) {
            System.out.println("This Email is not valid, Please enter another email");
            temp_email = sc.next();
        }
        this.email = temp_email;
    }

    private String Encryption(String PlainText)//ahmed
    {
        String CipherText = "";
        // aaa ->> ddd   fff -> iii
        // hi -> kl -> hi
        // plaintext : zy123 -> ciphertext -> cb123
        // ahmed ASCII Table   104 > 97
        // a -> z
        // "ahmed123"        '1' -> 49
        // ahmed     'a' - 'a' = 0 + 3 = 3
        // 'a' + 3 = 97 + 3 = 100
        for (int i = 0; i < PlainText.length(); i++) {
            if (PlainText.charAt(i) >= 'a' && PlainText.charAt(i) <= 'z')//ahmed
            {
                int CurCharInNumberAfterShifting = ((PlainText.charAt(i) - 'a') + 3) % 26;//28 % 26
                int cipher = 'a' + CurCharInNumberAfterShifting;//97 + 28 = 125
                CipherText += (char) cipher;//Casting
            } else CipherText += PlainText.charAt(i);
        }
        return CipherText;
    }

    public void setPassword(String Password) {
        String CipherText = this.Encryption(Password);
        this.password = CipherText;/// ghtf15
    }

    public void LogIn(String em, String Pass)//login("[email protected]","zy")
    {
        String EncryptedText = this.Encryption(Pass);
        if (this.email.equals(em) && this.password.equals(EncryptedText)) {
            System.out.println("Welcome Back," + this.name);
        } else {
            System.out.println("Not Authorized, Please Try Again");
        }
    }

    public String getEmail() {
        return this.email;
    }

    public String getPassword() {
        return this.password;
    }
   
    public int getNumOfAcc() {
        return NumOfAcc;
    }
}
  • Main.java file
import BankSystem.BankAcc;
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        // Inputs from the user
        String name = sc.next();
        int age = sc.nextInt();
        double balance = sc.nextDouble();
        String Password = sc.next();

        BankAcc Ahmed = new BankAcc(name, age, balance, Password);
        Ahmed.LogIn("[email protected]", "ahmed123");// Authorized
        Ahmed.LogIn("[email protected]", "ahmed12");// Not Authorized
        System.out.println("Num Of Created Accounts : " + Ahmed.getNumOfAcc());
    }
}
/*
arafat
23
1000
ahmed123

[email protected]
 */

Problem #2 :

create a class called Calculator that has three attributes [num1-num2-sign] where they are all inaccessible outside that class, then create a constructor that initialize them then create 4 methods each calculate the sum()/min()/div()/multi(), they are all private. Then create another method called Calc() which contains a switch statement that check value of [sign] then returns the value, then create another method that prints the value along the text

Problem #3 (Enhanced Problem #2) :

create a class called Calculator that has three attributes [num1-num2-sign] where they are all inaccessible outside that class, then create a constructor that initialize them then create 4 methods each calculate the sum()/min()/div()/multi(), they are all private. Then create another method called Calc() which contains a switch statement that check value of [sign] then returns the value, then create another method that prints the value along the text