User Exit and Customer Exit - Interview Questions

what is diff b/w user exits and customer exits

User Exits: 

1.These are forms, so they are called by sap 

standard programs using perform.

2. Inside the form you can read and change almost any 

global data from host program.

3. User exits doesn't have any classification.

4. These are basically destined for SD module only

Customer Exits: 

1. These are functions, so they are called 

using call functions.

2. Inside the function you can only access your 

import/export/changing/table/parameters

3. These exits have function, module, screen exits.

4. These are available for MM, SD, FI, hr almost for all 

Modules.

User Exit Characteristics:

1.A user exit is a three character code that instructs the system to access a program during system processing.SXX: S is for standard exits that are delivered by SAP.
XX represents the 2-digit exit number.UXX: U is for user exits that are defined by the user. XX represents the 2-digit exit number

2.USER EXITS are FORMS and are called by SAP standard programs
using PERFORM.
3.Inside the form (user exit) you can read and change almost
any global data from host program.

4. User exits are more flexible because you have more information to use in your code but on the other hand , it is very easy to manipulate erroneously global data and lead the standard program to a dump or even to make database inconsistent.

5.While changing User-exit,Access Key is required,

In user exits Usually global variables are used.

So this has disadvantage that if two or more user exits access the same global variables then the data or result may be erroneously interpreted.

So to overcome this in Customer exits the exits were defined in the form of function modules,therefore the exit can access only the variables that have been declared in their import,export or tables parameters thereby limiting the access to global variables.

Customer Exit Characteristics:

Due to the disadvantages they faced in the user exits (data can be interpreted erroneously) ,then SAP introduced the concept of Customer Exits.

1.   The R/3 enhancement concept allows you to add your own functionality to SAP’s standard business applications without having to modify the original applications. SAP creates customer exits for specific programs, screens, and menus within standard R/3 applications. These exits do not contain any functionality. Instead, the customer exits act as hooks. You can hang your own add-on functionality onto these hooks.

2.   CUSTOMER EXITS are FUNCTIONS so they are called using CALL
FUNCTION (or more exactly CALL CUSTOMER FUNCTION).

3.   Inside a function (customer exit) you can only access your import/export/changing/tables parameters.

4.   Customer exits are more restrictive but you are sure any change you can make to any parameters will never lead to inconsistency

5.   in Customer-exit no access key is needed.

Also since the custom coding done as part of these customer-exits is located away from the original SAP code, the maintenance is easier than user-exits.