What is exactly use of module pool

Question

hi guru.
please tell me in real time exactly what is the use of module pool programs.
thanks.
subhasis.

Answer 1

Module pools are directly created using the ABAP Editor and are introduced with the PROGRAM statement. With the exception of reporting event blocks and function modules, module pools can contain all processing blocks supported in ABAP and as many local classes as required. While they are executed, all events of the ABAP runtime environment may be triggered.  
The most important technical attribute of a module pool is that it can only be controlled using screen flow logic. You must start them using a transaction code, which is linked to the program and one of its screens (initial screen). Another feature of these programs is that you must define your own screens in the Screen Painter (although the initial screen can be a selection screen).
When you start a program using a transaction code, the runtime environment starts a processor that calls the initial screen. This then calls a dialog module in the corresponding ABAP program. The remainder of the program flow can take any form. For example, the dialog module can:
·        return control to the screen, after which the processing passes to a subsequent screen. Each screen has a following screen, set either statically or dynamically. Screens and their subsequent screens are components of freely definable screen sequences.
·        call other screen sequences, selection screens or lists, from which further processing blocks in the ABAP program are started.
·        call other processing blocks itself, either internally or externally.
·        call other application programs using CALL TRANSACTION or SUBMIT.
It is appropriate to use module pools when you write dialog-oriented programs using a large number of screens whose flow logic largely determines the program flow of screen sequences.