Publishers of technology books, eBooks, and videos for creative people

Home > Articles > Web Design & Development > Usability

  • Print
  • + Share This
This chapter is from the book

Working with Inheritance

Frequently it is useful to have components that implement similar functionality in different ways. For example, you might have a circle component and a square component. Each has a draw method: The circle component draws a circle on the screen, and the square component draws a square. Each also has independent properties: for example, the circle has circumference, and the square has length. The two components also have a lot in common: They each have perimeter and area. The square and circle components are special cases of a shape; they have everything a shape has, plus more. Thus, it would make sense to create a single parent component called shape that has the information that is common to all types of shapes, and to have child components that inherit this information and also add their own. Thus, square, as a child of shape, would have all the things that shape has plus length, and it would implement its own variation of draw.

Just as we can use the word my to refer to a CFC's THIS scope ("my ID is 123 and my First Name is Fred..."), in inheritance, we can think of the words is a. A square is a shape. An actor is a person. A cat is a mammal. In these cases, actor, square, and cat are children of person, shape, and mammal. Some parents can exist by themselves; there can be a person who is not an actor. Some other parents, though, are abstract; shape can't draw itself without knowing what shape it is. Rather, the parent is intended as more of a handy template upon which more specific things can be based.

In a movie studio application, actors and directors are both types of people, with some properties that are common and some that are unique. So, for types of people, you could create a component to represent a person and have each of these variants inherit from it.

Listing 27.2 shows the basic person component. It has a first name and last name (stored in the THIS scope) and has one function that "shows" the person by outputting the first and last name.

Listing 27.2. person.cfc—The Basic person Component

  Component that contains a "person", firstname and lastname only
  Modified by Ken Fricklas (
  Modified: 8/1/2007
  Code from Listing 27.2
<cfcomponent displayName="Person" hint="Parent Component - Person">

<cfparam name="THIS.firstName" default="John">
<cfparam name="THIS.lastName" default="Doe">

<cffunction name="showPerson" output="true" hint="showPerson in person.cfc" >
  <B>#THIS.firstName# #THIS.lastName#</B>


A component inherits from a parent component with the EXTENDS attribute of the <cfcomponent> tag. The value of the attribute is the name of the component upon which the new component should be based. Thus, a director component could consist of nothing more than this code:

<cfcomponent displayName="Movie Director" extends="person">

Now, the director is an exact copy of the person component and has inherited all the properties and methods of its parent. A CFML page, then, could create an instance of the director and invoke the methods of the person component as though they were part of the director component:

<cfobject component="director" name="myDirector">

Overriding Properties and Methods

Just because the parent does something doesn't mean that the child is stuck with it. The component can override parts of the parent component. If we want the director component to set the firstName and lastName properties to different values than those of the person component, we simply add code that redefines the values. The director, because it's the one being invoked, will take precedence. So the director component is now coded like this:

<cfcomponent displayName="Movie Director" extends="person">
  <cfset THIS.firstName = "Jim">
  <cfset THIS.lastName = "Jarofmush">

When invoked from the CFML page, this component now will output "Jim Jarofmush" instead of "John Doe". The THIS scope assignments made in a child override those of its parent. Likewise, adding a showPerson function to the director component will override the showPerson function from the parent:

<cffunction name="showPerson" output="true" hint="showPerson in director.cfc">
  <B>A swell director named #THIS.firstName# #THIS.lastName#</B>

Using the SUPER Scope

What if a child component needs to use the functionality in a method in its parent, but it has redefined that method already? In our director component, we could call the parent showPerson method, but we want to add our own information to it. We do this with the special scope SUPER. SUPER acts similarly to THIS, but instead of referring to a property or method in the current component, it refers to the property or method in the component's parent. We could redefine showPerson in the director component like this:

<cffunction name="showPerson" output="true" hint="showPerson in director.cfc">
  <B>A swell director</B> - #super.showPerson()#

This code calls the showPerson method in the person component.

In addition to the child's being able to invoke functions that are really part of the parent component (and overriding them, if desired), the parent can call functions that are part of the child by referencing them in the instance's THIS scope. Say we added a function called showDetail to the director component:

<cfset THIS.credits = arrayNew(1)>
<cfset THIS.credits[1] = "The Phantom Dentist">
<cfset THIS.credits[2] = "Austin Showers">
<cfset THIS.credits[3] = "Men in Slacks II">

<cffunction name="showDetail" output="true">
  Credits include:
  <cfloop index="i" from="1" to="#arrayLen(THIS.credits)#">

We could then modify the showPerson function in the person component to optionally call showDetail:

<cffunction name="showPerson" output="true" hint="showPerson in person.cfc">
  <cfargument name="showDetail" required="false" type="boolean"
  <B>#THIS.firstName# #THIS.lastName#</B>
  <cfif arguments.showDetail>

Since the director component wants the showPerson method to call its showDetail method, we change its showPerson method to pass in this argument, like this:

<cffunction name="showPerson" output="true" hint="showPerson in director.cfc">
  <B>A swell director</B> - #super.showPerson(true)#

In the calling template now, we can call the showPerson function in the director component:

<cfobject component="director" name="myDirector">

The result of our showPerson function now will be a combination of showPerson from the person component and showDetail from the director component:

A swell director - Jim Jarofmush
Credits include:
. The Phantom Dentist
. Austin Showers
. Men in Slacks II

This technique can be useful when multiple components are descendents of the same parent but require slightly different methods. Say we based an actor component on the same "person" parent using this code:

<cfcomponent displayName="Movie Actor" extends="person">
  <cfset THIS.firstName = "Judi">
  <cfset THIS.lastName = "Dents">

<cffunction name="showDetail" output="true">
  Star of the hit <EM>The Importance of Being Sternest</EM>.


When the showPerson function is invoked, the appropriate showDetail function is used, depending on whether the component is an actor or director (see Listing 27.3).

Listing 27.3. index.cfm—Calling Components to Show Inheritance

<!--- instantiate an actor and a director --->
<cfobject component="director" NAME="myDirector">
<cfobject component="actor" NAME="myActor">
<!--- demonstrate that showPerson calls different showDetail functions for each --->
  Directed by:<br>
    #myDirector.showPerson()# <!--- overridden in the director component --->
    #myActor.showPerson(true)# <!--- must pass argument true to have the showPerson
call showDetail, since it's not overridden --->

This code results in this output:

Directed by:
A swell director - Jim Jarofmush
Credits include:
. The Phantom Dentist
. Austin Showers
. Men in Slacks II
Judi Dents
Star of the hit The Importance of Being Sternest.

Must you use inheritance in your ColdFusion applications? Certainly not. But it can be very useful in ways similar to other code-reuse techniques. Components can be built-in "branches," as in a family tree with chains of ancestral parent components, each providing base functionality to their children.

Component packages can help with this type of organization, too, to make applications more easily maintainable. In that case, the extends="..." attribute uses the same package path syntax as a <cfinvoke> tag. For example, to inherit from a component called "person" in the package myApp.components, the <cfcomponent> tag would be coded like this:

<cfcomponent extends="myApp.components.person">
  • + Share This
  • 🔖 Save To Your Account

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Peachpit products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive:

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020