Confused with Java Encapsulation Concept

Question

Good day!

I am reading a Java book about encapsulation and it mentioned the getter and setter method.

I've read that to hide the attributes, I must mark my instance variables as "PRIVATE" and make a "PUBLIC" method of getter and setter to access the data. So I tried making a similar but not the conventional code about it as follows:

public class AddressBookEntry {

    private String name;
    private String address;
    private String telNo;
    private String email;

    public void getAllInfo() {
        name = JOptionPane.showInputDialog("Enter Name: ");
        address = JOptionPane.showInputDialog("Enter Address: ");
        telNo = JOptionPane.showInputDialog("Enter Tel. No: ");
        email = JOptionPane.showInputDialog("Enter Email Address: ");
    }
}

Does my code above exposes my variables because I assigned it directly? How can I do this better? Would it be better if I make the conventional getter and setter method instead and assigned the values on the other class? What does "hiding the data" means?

Thank you.

Answer 1

You use setters and getters to make the variables accessible from outside your class. In your example you will have

public class AddressBookEntry {

    private String name;

    public void setName(String name) {
       this.name = name;
    }

    public String getName() {
       return name;
    }
}

You will access the name property from a UI class (it isn't good to mix UI and business logic in the same class):

public class MyPane extends JFrame {

  public getAllData() {
     String name = JOptionPane.showInputDialog("Enter Name: ");
     AddressBookEntry entry = new AddressBookEntry();
     entry.setName(name);
     // You can't use entry.name = name
  }

}

Answer 2

Yes and no. The point of encapsulation is that it prevents other classes from needing to know what your class is doing behind the scenes. If you store your name in a String (as you've done here), read/write it from a file, or do something different, the point of encapsulation is that to the user of your class it doesn't matter because all they see is String getName( ) and void setName (String name).

Since the modification of the data is entirely under the control of your class here, it doesn't break encapsulation. If you did store name to file, then you could potentially do so in getAllInfo without any other user of the class being any the wiser. Since the observable behaviour from the outside of the class still hides what the internals of the class is doing, it's still encapsulated.

That said, this is a very unconventional approach. Like I describe in the first paragraph, use of accessor methods (getters and setters) is a more idiomatic approach, and easier to understand for someone else using your code. You can do what you do, it doesn't break encapsulation, but it's not what I'd call elegant or typical.