What is the difference between standard controllers and custom controllers?
The standard controller is auto geenrated by SF for all objects. Custom controllers are written by you and do what your code tells them to do.
What is a requirement for a class to be used as a custom Visualforce controller?
There are a lot of system and utility classes to help you write custom controller logic, but the only requirement for a class to be used as a custom controller is that it exists.
Are there any extension methods with the same name?
The extension class has a method with the same name as a method in the standard controller will this call the method from the standard controller or the extension? Any extension methods take precedence over controller methods with the same name. Take a look at Building a Controller Extension:
Which is an example of a controller extension?
A controller extension is any Apex class containing a constructor that takes a single argument of type ApexPages.StandardController or CustomControllerName, where CustomControllerName is the name of a custom controller you want to extend. The following class is a simple example of a controller extension:
What happens when a controller extends a standard controller?
However, if a controller extension extends a standard controller, the logic from the standard controller does not execute in system mode. Instead, it executes in user mode, in which the permissions, field-level security, and sharing rules of the current user apply.
Can you use an extension method on an interface?
You can use extension methods to extend a class or interface, but not to override them. An extension method with the same name and signature as an interface or class method will never be called. At compile time, extension methods always have lower priority than instance methods defined in the type itself.