Specifying private on the employeeId member variable has created a problem.

We not only prevented the outside class from editing employeeId, we also prevented the outside class from reading employeeId. Accessing this member variable via the dot operator will yield a compilation error:

public class EmployeeController {
      Employee newEmp = new Employee(); 
      String  empId = newEmp.employeeId;
      // Compilation Failure: Variable is not visible: Employee.employeeId
}

The sky is falling! Let’s modify the Employee class so that employeeId can be read but not set by outside classes. How? With Apex Properties, baby!

There are a few different properties out there - for now, we’re just going to talk about automatic properties. You can read about the others here if you’re up for it.

Properties automatically execute when a member variable is set or retrieved via accessors. When variables are set using the dot operator, they’re implicitly calling the set accessor. When values are retrieved using the dot operator, they’re implicitly calling the get accessor.

But how can we use property accessors to solve our problem? Well, we can use access modifiers on property accessors. 🤯 Yeah, you read that right.

Rewriting Employee would look like this:

public class Employee {
      public String employeeId { get; private set; }
        
      public Employee(){
            this.employeeId = // fancy logic that sets employee id 
      }
}

The accessor must be more restrictive than the member variable itself. If it's not, you'll receive a compilation error saying Cannot declare public accessor on private property. In our case, employeeId will be public for get (because the access modifier on employeeId is inherited) and it will be private for set.

This solves our problem! Now, EmployeeController can read employeeId from an Employee object but cannot set it.

public class EmployeeController {
      Employee newEmp = new Employee();
      String empId = newEmp.employeeId; // this works now!
      // newEmp.employeeId = ‘INVALID ID skdhgkjsdf’; This would still cause a compile error (which is what we want) 
}