Let me answer this question for you:
The basic rule in SAP as far as ABAP workbench developments are concerned is "Do not modify the source code of the program"
Since needs and requirements keep on changing from client to client and for various business scenarios, there is a need to customise the programs as per client requirement.
For this purpose, SAP has provided numerous list of user-exits also known as enhancements, which is nothing but a program which will deal with the client additional requirement, without modifying the source code of the program. These exits are already provided by SAP. You can see the list of user-exits provided by using the transaction code SMOD. If you cannot find an user exit which match with client requirements, then you can tell SAP to create a new user exit.
On the other hand, field exit is nothing but where you write a small program, to control the properties of an existing field in a particular screen. Hence creation of a field exit is controlled by Program name, screen no. and the field name.
To give you an example, if you want to prevent a particular payment method to be executed via transaction FBZ5 or F-58, such that if the user enter a particular payment method while executing the transaction FBZ5 or F-58, the system should restrict the user from proceeding further, u can write a field exit for field RZAWE (payment method).
The program which controls the creation of field exit is RSMODORF
As far as screen exit is concerned, as per the client
requirement if the user wants a separate screen to appear on execution
of a particular task, which deviates from the standard sap provided flow
of transactions, you write a screen exit. In such case you first
prepare the screen using the screen painter and define it as to after which
sap screen you want this screen to appear for processing the transaction
further.
What is user exit and custome user exit?
USER EXIT:
It is nothing but adding some additional logic to the standard logic, without disturbing the standard logic is always through sub routines.
CUSTOMER EXIT:
It is nothing but adding some additional logic to the standard logic, without disturbing the standard logic is always through function modules.
Customer exits are divided into 4 types.
|
| ----- Screen Exit ---> Adding some
additional sub screen to the standard screen.
| ----- Menu Exit. ---> Adding
some additional menus to the standard menu.
| ----- Function Exit ---> Adding
some additional logic to the standard function.
| ----- Field Exit ----> Used to change
the text of input field or provided the extra validation to the field.
