3 User Exits on Material Master via MM01/MM02 tcode
When your have requirement that the standard material can’t provide, you can use user exits on material master to add your ABAP Code.
There are 3 user exits available for Material Master : MGA00001, MGA00002, MGA00003, we’ll go to over each of these user exits.
User Exit MGA00001
User Exit MGA00001 allows extra checks to be made of the data that is entered or changed in material master data via transaction MM01 or MM02, this user exit run both for material master creation or change.
For example when you need to add checking to the field is not normally checked when material master is created such as STORAGE BIN field wouldn’t occur error in the standard transaction but you can use this user exit to add your ABAP code to entered your logic for checking any field.
User Exit MGA00002
User exit MGA00002 is a user exit that allows a company to change the way the material number when a material created. this user exit useful if your user wants to add checking logic and add the code to the material number that is being entered.
MGA00002 user exit can alse be used if your client wants to assign a material number generated by your custom program based on their specific needs.
User Exit MGA00003
MGA00003 is a user exit in the material master that can be used to allow material number to be displayed in a particular format rather than standard SAP format.
For example, you need to add character JXXX to material number at display time such as JXXX-123456. However JXXX- prefix is added to material number at display only, while just the 123456 is stored in SAP as the material number.
So if you want to more understand in ABAP, I Highly recomended that you check out SAP ABAP Tutorial