A ColdFusion component (CFC) is a file saved with the extension .cfc. A CFC can contain data and functions. Within a CFC, data is referred to as properties. Although you use the cffunction tag to define functions within a CFC, they are typically referred to as methods instead of functions.

The page on which you define a CFC is also known as a component page. Component pages use the same tags and functions that regular CFML pages do, plus a small number of special tags (in particular, the cfcomponent tag) and tag attributes.

You define related methods in a CFC. Unlike ColdFusion custom tags, a single CFC can perform many related actions, defined in multiple methods. The methods may share a data context, such as metadata and scoping, or manage a particular database or set of tables. For example, you can define the methods to insert, update, delete, and retrieve records from a particular database or table in one CFC.

CFCs and object-oriented programming

CFCs are building blocks that let you develop ColdFusion code in an object-oriented manner, although CFCs do not require you to do object-oriented programming. Some of the object-oriented features of CFCs include encapsulation, inheritance, and introspection. CFC object-oriented features are similar to the object-oriented elements in other languages, like JavaScript.

The technique of incorporating both code and data into one object such as a CFC is known as encapsulation. Encapsulation lets users pass data to and get a result from your CFC without having to understand the underlying code. When you use encapsulation, you can validate data that is passed to the CFC. CFCs can also enforce data types, check for required parameters, and optionally assign default values.

One CFC can inherit the methods and properties of another CFC. Inheritance lets you build multiple specific components without rewriting the code for the basic building blocks of the components. For more information, see Using the Super keyword.

CFCs support introspection; that is, they can provide information about themselves. If you display a component page directly in an HTML browser, inspect it in the ColdFusion and Adobe Dreamweaver CS3 component browsers, or use the CFML GetMetadata function, you see information about the component. This information includes its path, property, methods, and additional information that you can specify using special documentation attributes and tags. For more information, see Using introspection to get information about components.

When you use a ColdFusion component, you can simply invoke a method in the CFC. However, typically, you create an instance of the CFC, and then invoke methods and refer to properties of the CFC.