2.4.6 How to Define Private Fields

• Encapsulation (22:21)
• The Private Visibility Modifier (17:38)
• The Benefits of Encapsulation (6:56)

The private visibility modifier and encapsulation go hand in hand. By making members of a class private it limits the ability of them to be used by only the current instance of the class. This prevents other objects from being able to interact with the members of another object. It protects and locks down data so that the only things 'close' to an object can use it.

Private Field Values

To make a field private, simply change the public on a field definition to private. Since we only want the Employee to be controlling their HoursWorked let's make that field private.

So now in the MainWindow where we are assigning the attendant's hoursWorked it is throwing an error because the MainWindow shouldn't be able to do anything to a field the Employee should handle themselves.

Private field references

Let's make the Employee's Weight field private as well.

Notice that when we do this, a reference to the Weight field in the Burp method throws an error. This is because the application is looking for a field with a capital letter but not finding one.

We can fix this error by changing the reference from an upper case to a lower case.

Because the Burp method is in the same class as the private weight field it can access it directly.

Private fields in class/sequence diagrams

Anything public in class/sequence diagrams has been represented with a + sign. Private fields, however, are represented using a - sign.

Let's take a look at the changes made so far:

To represent this in a class diagram would look like this:

Notice how the casing is now lower case, the + is now a -, and the fields have shifted below the public fields.