.NET Tip: Data Encapsulation: Using Properties Instead of Public Variables

I have run across some old code recently where some classes exposed public variables directly to the outside world. Even though the code works, it is very fragile. The code looked something like this:

public class Person
{
   public string Name;
   public int Age;
}

A much better practice is to make class variables private and expose them through public properties, thus encapsulating the details of your implementation. This brings several benefits, including that ability to override the property in derived classes or to easily add validation logic when the property value is set. You also can create calculated properties whose values are determined only when they are accessed. A version of the Person class using properties might look like this:

public class Person
{
   private string _Name;
   private int _Age;

   public string Name
   {
      get { return _Name; }
      set { _Name = value; }
   }

   public int Age
   {
      get { return _Age; }
      set { _Age = value; }
   }
}

As you can see, using properties does take several more lines of code than exposing public variables. The cost, though, is well worth the benefit to your application. If you are using Visual Studio 2008, you can use the new support for the automatic properties to gain the benefit of properties with syntax that is very similar to using public variables. Here is the Person class in Visual Studio 2008 using automatic properties:

public class Person
{
   public string Name { get; set; }
   public int Age { get; set; }
}

In the long run, I think you will find that using properties makes your classes more stable and easier to extend.

About the Author

Jay Miller is a Software Engineer with Electronic Tracking Systems, a company dedicated to robbery prevention, apprehension, and recovery based in Carrollton, Texas. Jay has been working with .NET since the release of the first beta and is co-author of Learn Microsoft Visual Basic.Net In a Weekend. Jay can be reached via email at jmiller@sm-ets.com.



Comments

  • More meat in the article please

    Posted by corwin_ranger on 09/17/2007 03:01pm

    As a suggestion. You bring up a good point in this article, but you need to add a bit more meat to make it useful to someone who'd new to programming, or has been using the public variable method to attain the same result. For example, you say that using public variables makes your code more fragile, someone who just looks at the small code examples and isn't familiar with properties would never know WHY public variables make for more fragile code. Tell them. Your examples should probably be a bit more detailed as well. There's virtually no value in using properties in the way you've described. You add a bunch of code, but get nothing for it. Use the opportunity to show how error correction, additional type safety, range validation, etc...can be built into the property code. Now someone can see a value in adding the code. Hope you find this criticism constructive, as it was intended to be. Steve

    Reply
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