Object Oriented C# for ASP.NET Developers

Essential Jargon

Writing .NET applications (be they Windows desktop applications or ASP.NET Web applications) is all about constructing a web of interrelated software components that work together to get the job done. These components are called objects.

There are many different kinds of objects, and in fact a big part of programming in .NET is creating your own types of objects. To create a new type of object that you can use in your .NET programs, you have to provide a blueprint of sorts that .NET will use to create new objects of this type. This blueprint is called a class.

Let's look at a conceptual example to help these ideas take hold. Say you worked for the National Forestry Commission, and your Web site needed to keep track of a group of trees in a forest; specifically, say it needed to keep track of the heights of those trees. Fig 1 shows an example of the class and objects that you might create as an ASP.NET programmer working on this site.

On the left we have a class called Tree. This class defines a type of object -- a Tree -- that will serve as the blueprint from which all Tree objects will be created. The class itself is not a Tree; it is merely a description of what a Tree is, or what all Trees have in common. In this example, our Tree class indicates that all Trees have a property called 'height'.

On the right, we have two actual Tree objects. These are Trees, and they were created based on the blueprint provided by the Tree class. These objects are said to be instances of the Tree class, and the process of creating them is called instantiation. Thus, we can say that by instantiating the Tree class twice, we have created two instances of the Tree class, two objects based on the Tree class, or just two Trees. Notice that in creating these objects we have assigned a value to their height property. The first Tree is 2 meters high and the second is 5 meters high. Although the values of these properties differ, this does not change the fact that both objects are Trees. They are simply Trees with different heights.

Classes don't only define properties of objects; they also define operations that may be performed by those objects. Such operations are called methods in object-oriented languages like C#. Continuing with our Tree example, we could define a method called 'Grow' in the Tree class. The result of this would be that every Tree object would then be able to perform the Grow operation as defined in the class. For instance, performing the Grow operation on a Tree might increase its height property by one metre.