Let’s start of with a piece of code.
We have a Main( ) method, which creates an object of a Circle class, sets the radius and then calculates the area of the circle. Let’s have a look at the circle class. It has a simple implementation to calculate the area of circle.
The above code looks simple and it works. Are there any flaws in it? Let’s examine.
What if the consumer of the Circle class, does not set the radius correctly? For example, like this,
circle.Radius = Convert.ToInt32("abc");
The call to CalculateArea( ) would fail, because the input cannot be parsed into an integer. By design, the Circle class is allowing other classes to control the Radius property. The consuming classes, may set unacceptable values for the Radius property. This leads to unpredictable results from the CalculateArea( ) method. We can do a validation check for the Radius property either in it’s setter or the CalculateArea( ) method. That would work. Perhaps that is a natural approach we adopt most of the time.
But let us for a moment take a step back and think more in terms of object orientation. Imagine someone asks you to draw a circle on a piece of paper. Your obvious question would be, “Sure, how big or small do you want it?”. In other words, in order to “construct” a circle, you would need the information about it’s radius.
One more important aspect in this example, is that a Circle is immutable. Once we create circle with a certain radius, we cannot change it. Making the setter for Radius property as public allows the consuming classes to alter it, even after it has been created (Hmm, not good.)
It is therefore always a good idea to create objects in a robust way, when they are being constructed. The radius property is integral to the Circle class and it is the responsibility of Circle class to manage it. The clients just need to provide the details while creating the objects. If the client code provides incorrect information while constructing the object, the class can choose not to go further with its creation, thereby protecting its integrity.
In addition, once we make a property as public, it is very difficult to make it private again, because by the time you realize that you need to do that, there may be a number of places, it has already been consumed and used in different ways.
As a thumb rule, try to restrict the access to all the properties in the class when you write it for the first time. This will allows you to encapsulate the class properties and the code to manage them inside the class itself. If you need to make any property as protected, internal or public, think and try to find for a strong need and justification for doing so.