Can anyone compare and contrast custom controllers & controller extensions in Salesforce?

Hello Chanchal,

Standard controllers can often provide all of the functionality and data that you need for your Visualforce page.

However, you may need to start coding your own controller code if you want then its Custom controller

1. Override existing functionality
2. Make new actions available to the page
3. Customize the navigation
4. Use HTTP callouts or web services
5. Have greater control of how information is accessed on the page

Controller Extension

If you want to keep most of the functionality of a standard or custom controller it is wiser to have an extension

controller extension can extend standard or custom controller.

Thanks.

Controller extension is very useful and important concept introduced by the salesforce recently. It gives the power to programmer to extend the functionality of existing custom controller or standard controller.
A Visualforce can have a single Custom controller or standard controller but many controller extensions.
we can say that the custom extension is the supporter of custom or standard controller.

If you want to use completely custom functionality and don't really need most of the standard object behaviors, custom controller is a good option, but bear in mind, any standard actions you want to use will have to be implemented in your custom class. A page with a custom controller would use the following attribute:

<apex:page controller="MyApexClass"...> ... </apex:page>

Consider one example : If there is one controller written and used by the multiple visualforce pages and one of them needs some extra logic. Then instead of writing that logic to controller class (Which is used by many visualforce pages) we can create a controller extension and apply to that page only.