User exits and types

What are User Exits? What are different types of User Exits in Oracle Apps? Explain the types.

A user exit is a C subroutine written by user and called by Oracle Forms to do special-purpose processing. Helps the User to exit from the current working environment.
Types of User exit:

FND SRWINIT: Sets your profile option values and allows Oracle AOL user exits to detect that they have been called by an Oracle Reports program.

FND SRWEXIT: Ensures that all the memory allocated for Oracle AOL user exits has been freed up properly.

FND FORMAT_CURRENCY: Is used for MULTIPLE CURRNECY REPORTING.FND FLEXIDVAL: This API is used for get descriptions from flexfields get input from FND FLEXSQL.

FND FLEXSQL: This API is used for get ELECT/WHERE/HAVING/ORDER BY/GROUP BY from flex field tables.