List of Questions on BAPI and OOPs

Question

Hi All,
   I am new to the OOPs and BAPI's.can any one gives me complete idea on below questions by providing good examples.
1) Importance of the class, Interface type, Object and Instance ?
2) Why we need oops concepts since we are using normal process successfully, i mean with out oops also ?
3) functionality of BAPI ?
4) Difference between COMMIT WORK and BAPI_TRANSACTION_COMMIT ?
5) Why COMMIT WORK wont useful for BAPI's ?
6) If you give me good source code to understand the concepts of class, Interface type, Object and Instance?
7) In real time situations, do we need to create classes or in SAP we will use only existed bapis?
8) The process of creating customized BAPI's [entire scenario]
Since i asked lot of questions in one thread, i decided to give rewards even if you provide me solution for any of the above.
Thanks
Jaya

Answer 1

Hi Jaya,
Answer 1. Class is a template for creating objects. Object can also be called as instance.
Interfaces allow you to use different classes in a uniform way (polymorphism).
Answer 2. Normal abap is a procedural programming where as by using abap objects we can achieve object oriented programing.
Answer 6. Source code:
In below code i have created a interface and a class which is implementing the interface. I have declared a reference variable of type interface and created a object. Then i have called a method.
REPORT  ZABAPOBJECTS_INTERF.
      INTERFACE I1
INTERFACE I1.
  METHODS METH1.
ENDINTERFACE.                    "I1
      CLASS C1 DEFINITION
CLASS C1 DEFINITION.
  PUBLIC SECTION.
    METHODS: METH2.
    INTERFACES: I1.
ENDCLASS.                    "C1 DEFINITION
      CLASS C1 IMPLEMENTATION
CLASS C1 IMPLEMENTATION.
  METHOD I1~METH1.
    WRITE: / 'This is a method one'.
  ENDMETHOD.                                                "I1~METH1
  METHOD METH2.
    WRITE: / 'This is a method two'.
  ENDMETHOD.                                                "METH2
ENDCLASS.                    "C1 IMPLEMENTATION
START-OF-SELECTION.
  DATA : REF1 TYPE REF TO I1.
  CREATE OBJECT REF1 TYPE C1.
  CALL METHOD REF1->METH1.
Question 7: Yes we need to create a class but most probably we use the existing classes.
Regarding BAPi's go through the below links,
http://www.sapgenie.com/abap/bapi/example.htm
http://www.sapdevelopment.co.uk/bapirfc/bapirfchome.htm
Regards,
Azaz Ali.