Introduction to Encapsulation

What is Encapsulation ?

Encapsulation is a way of keeping data safe inside a class. It means we hide the details of how something works and only allow access through special methods (getters and setters). This helps protect data from unwanted changes, makes the code easier to manage, and keeps everything organized.

Why is Encapsulation Important?

Encapsulation is important because it helps protect data and keeps a program organized. By making variables private, we prevent them from being changed directly from outside the class. Instead, we use getters and setters to control how data is accessed or modified. This reduces the risk of errors, makes debugging easier, and allows changes to be made without affecting other parts of the program.

as an example, imagine a Bank Account class. If the balance variable is public, anyone can change it freely, even setting a negative balance. With encapsulation, we make it private and allow updates only through a setBalance() method that checks if the value is valid.

let’s learn Encapsulation in Java

Let's look at an example scenario of a bank account and create a bankAccount class and try to print some data in the bankAccount class

class BankAccount{
   private int bankBlance;
   private String ownersName;
   private int accountNumber = 741852;


}
public class Main  {

        public static void main(String[] args) {
            BankAccount bankAccount= new BankAccount();
            System.out.println(bankAccount.accountNumber);
        }
    }

Output = Main.java:6:43 java: accountNumber has private access in BankAccount

Why this happened ?

code will produce a compilation error because the accountNumber variable is private in the BankAccount class. Since private variables cannot be accessed directly from outside the class, the following line will cause an error:

Then how can we access the accountNumber?

That's where getters and setters come into play. We can use methods to set values for the private variables and use get methods to retrieve values from these variables. Here's how it works

public class Main  {

        public static void main(String[] args) {
            BankAccount bankAccount= new BankAccount();
            System.out.println("old Account Number "+ bankAccount.getAccountNumber());
            bankAccount.setAccountNumber(1000);
            System.out.println("New Account Number "+ bankAccount.getAccountNumber());

        }
    }

class BankAccount{
   private int bankBlance;
   private String ownersName;
   private int accountNumber = 741852;

    public int getAccountNumber() {
        return accountNumber;
    }

    public void setAccountNumber(int newAccountNumber) {
        accountNumber = newAccountNumber;
    }
}

Output =

old Account Number 741852

New Account Number 1000

As you can see, I can now access the accountNumber variable inside BankAccount using the public method getAccountNumber(). I can also change its value to a new account number by passing data as a parameter to setAccountNumber(1000).

insted of typing all this getters and setters we can use out IDE code editors to auto genarate getters and setters for us this is how you can do it

No need to write getters and setters manually in a tedious way - use your IDE to generate them automatically.

step 1 - I use IntelliJ, and the process is similar for most other IDEs. Right-click on your class and find "Generate."

step 2- as below image show you can click on getters and setters option

step 3 - Now you can select the relevant variable that needs getters and setters, then click OK. All done!

Result

class BankAccount{
   private int bankBlance;
   private String ownersName;
   private int accountNumber = 741852;

    public int getBankBlance() {
        return bankBlance;
    }

    public void setBankBlance(int bankBlance) {
        this.bankBlance = bankBlance;
    }

    public String getOwnersName() {
        return ownersName;
    }

    public void setOwnersName(String ownersName) {
        this.ownersName = ownersName;
    }

    public int getAccountNumber() {
        return accountNumber;
    }

    public void setAccountNumber(int accountNumber) {
        this.accountNumber = accountNumber;
    }
}

What is this key word ?

Instead of explaining the this keyword, I'll show you a scenario of what happens if I stop using it and write the code above like this

public class Main  {

        public static void main(String[] args) {
            BankAccount bankAccount= new BankAccount();
            System.out.println("old Account Number "+ bankAccount.getAccountNumber());
            bankAccount.setAccountNumber(1000);
            System.out.println("New Account Number "+ bankAccount.getAccountNumber());

        }
    }

class BankAccount{

   private int accountNumber = 741852;

    public int getAccountNumber() {
        return accountNumber;
    }

    public void setAccountNumber(int accountNumber) {
        accountNumber = accountNumber;
    }
}

now no accountNumber = newAccountNumber i am jsut assigning accountNumber = accountNumber if i run this code the answer will be like this

output =

old Account Number 741852

New Account Number 741852

Oh, why are the old and new values the same? What happened here?

The old and new account numbers are the same because the setAccountNumber() method isn't actually changing the value. It's just assigning the accountNumber to itself, using the parameter sent to the function, and the parameter itself gets updated. and naver change the value of private int accountNumber = 741852;

This is how this key word used

By using the this keyword, we explicitly indicate that this.accountNumber refers to the instance variable of the BankAccount class, distinguishing it from method parameters or local variables with the same name. This ensures clarity and prevents unintended variable shadowing, making the code more readable and maintainable.

public class Main  {

        public static void main(String[] args) {
            BankAccount bankAccount= new BankAccount();
            System.out.println("old Account Number "+ bankAccount.getAccountNumber());
            bankAccount.setAccountNumber(1000,bankAccount);
            System.out.println("New Account Number "+ bankAccount.getAccountNumber());

        }
    }

class BankAccount{

   private int accountNumber = 741852;

    public int getAccountNumber() {
        return accountNumber;
    }

    public void setAccountNumber(int accountNumber) {
        this.accountNumber = accountNumber;
    }
}