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This blog represents part 2 of the 6-part series Getting comfortable using the Object-Oriented design model with ABAP.

Part 1 – Transforming a simple procedural model into its equivalent OO design, focusing on the OO principles of Encapsulation and Abstraction.

Part 2 – Exploring Abstraction further by refactoring the program to transform selected static classes into instantiable classes.

Part 3 – Refactoring the program further to take advantage of the OO principle of Inheritance.

Part 4 – Adhering to the Single Responsibility Principle by refining the program to restrict each class to do only what it is intended to do.

Part 5 – Removing classes that no longer serve a purpose.

Part 6 – Introducing the Singleton OO design pattern, resulting in elimination of all static classes.

To recap from the preceding blog, we took a procedural program and transformed it into one that uses local static classes and a local interface. Here is the source code as we left it in the previous blog:

report.
interface data_exchangeable.
  types          : row_counter    type n length 02.
  types          : email_recipient
                                  type adr6-smtp_addr.
endinterface.
class excel_spreadsheet_manager        definition
                                       abstract
                                       final.
  public section.
    class-methods: copy_table_to_excel_worksheet
                     importing
                       source_stack
                         type standard table
                       source_description
                         type string
                     raising
                       zcx_excel
                 , send_excel_via_email
                     importing
                       recipient
                         type data_exchangeable=>email_recipient
                 .
  private section.
    class-data   : excel          type ref to zcl_excel.
endclass.
class excel_spreadsheet_manager        implementation.
  method copy_table_to_excel_worksheet.
    constants    : first_column   type char1     value 'A'
                 .
    data         : worksheet      type ref to zcl_excel_worksheet
                 , worksheet_title
                                  type zexcel_sheet_title
                 , table_settings type zexcel_s_table_settings
                 .
    table_settings-table_style    = zcl_excel_table=>builtinstyle_medium2.
    table_settings-show_row_stripes
                                  = abap_true.
    table_settings-nofilters      = abap_true.
    table_settings-top_left_column
                                  = first_column.
    table_settings-top_left_row   = 01.
    if excel is not bound.
      create object excel.
      worksheet                   = excel->get_active_worksheet( ).
    else.
      worksheet                   = excel->add_new_worksheet( ).
    endif.
    worksheet_title               = source_description.
    worksheet->set_title( worksheet_title ).
    worksheet->bind_table(
      ip_table                    = source_stack
      is_table_settings           = table_settings
      ).
  endmethod.
  method send_excel_via_email.
    constants    : excel_file_type
                                 type string value '.xlsx'
                 , file_name_parameter
                                  type string value '&SO_FILENAME='
                 .
    data         : excel_writer   type ref to zif_excel_writer
                 , excel_as_xstring
                                  type xstring
                 , excel_as_xstring_bytecount
                                  type i
                 , excel_as_solix_stack
                                  type solix_tab
                 , mail_send_request
                                  type ref to cl_bcs
                 , mail_message   type ref to cl_document_bcs
                 , any_bcs_exception
                                  type ref to cx_bcs
                 , diagnostic     type string
                 , mail_title     type so_obj_des
                 , mail_text_stack
                                  type soli_tab
                 , mail_text_entry
                                  like line
                                    of mail_text_stack
                 , mail_attachment_subject
                                  type sood-objdes
                 , mail_attachment_bytecount
                                  type sood-objlen
                 , mail_attachment_header_stack
                                  type soli_tab
                 , mail_attachment_header_entry
                                  like line of mail_attachment_header_stack
                 , internet_email_recipient
                                  type ref to if_recipient_bcs
                 , successful_send
                                  type abap_bool
                 , file_name      type string
                 .
    " Much of the code here was lifted from method send_mail of
    " class lcl_ouput, defined in object ZDEMO_EXCEL_OUTPUTOPT_INCL:
    concatenate sy-repid          " this report name
                sy-datum          " current date
                sy-uzeit          " current time
                excel_file_type   " excel file extension
           into file_name.
    mail_title                    = file_name.
    mail_attachment_subject       = file_name.
    mail_text_entry               = 'See attachment'.
    append mail_text_entry
        to mail_text_stack.
    concatenate file_name_parameter
                file_name
           into mail_attachment_header_entry.
    append mail_attachment_header_entry
        to mail_attachment_header_stack.
    create object excel_writer type zcl_excel_writer_2007.
    excel_as_xstring              = excel_writer->write_file( excel ).
    excel_as_solix_stack          = cl_bcs_convert=>xstring_to_solix( iv_xstring = excel_as_xstring ).
    excel_as_xstring_bytecount    = xstrlen( excel_as_xstring ).
    mail_attachment_bytecount     = excel_as_xstring_bytecount.
    try.
      mail_message                = cl_document_bcs=>create_document(
                                      i_type    = 'RAW' "#EC NOTEXT
                                      i_text    = mail_text_stack
                                      i_subject = mail_title
                                      ).
      mail_message->add_attachment(
        i_attachment_type         = 'XLS' "#EC NOTEXT
        i_attachment_subject      = mail_attachment_subject
        i_attachment_size         = mail_attachment_bytecount
        i_att_content_hex         = excel_as_solix_stack
        i_attachment_header       = mail_attachment_header_stack
        ).
      mail_send_request           = cl_bcs=>create_persistent( ).
      mail_send_request->set_document( mail_message ).
      internet_email_recipient    = cl_cam_address_bcs=>create_internet_address( recipient ).
      mail_send_request->add_recipient( internet_email_recipient ).
      successful_send             = mail_send_request->send( ).
      commit work.
      if successful_send eq abap_false.
        message i500(sbcoms) with recipient.
      else.
        message s022(so).
        message 'Document ready to be sent - Check SOST' type 'I'.
      endif.
    catch cx_bcs into any_bcs_exception.
      diagnostic                  = any_bcs_exception->if_message~get_text( ).
      message diagnostic type 'I'.
    endtry.
  endmethod.
endclass.
class flight_report                    definition
                                       abstract
                                       final.
  public section.
    class-methods: produce_report
                     importing
                       row_count
                         type data_exchangeable=>row_counter
                     raising
                       zcx_excel
                 .
endclass.
class flight_report                    implementation.
  method produce_report.
    data         : flight_stack   type standard table of sflight
                 , alv_report     type ref to cl_salv_table
                 .
    try.
      call method cl_salv_table=>factory
        importing
          r_salv_table            = alv_report
        changing
          t_table                 = flight_stack.
    catch cx_salv_msg.
      return.
    endtry.
    select *
      into table flight_stack
      from sflight
             up to row_count rows.
    alv_report->display( ).
    call method excel_spreadsheet_manager=>copy_table_to_excel_worksheet
      exporting
        source_stack              = flight_stack
        source_description        = 'Flights'.
  endmethod.
endclass.
class carrier_report                   definition
                                       abstract
                                       final.
  public section.
    class-methods: produce_report
                     importing
                       row_count
                         type data_exchangeable=>row_counter
                     raising
                       zcx_excel
                 .
endclass.
class carrier_report                   implementation.
  method produce_report.
    data         : carrier_stack  type standard table of scarr
                 , alv_report     type ref to cl_salv_table
                 .
    try.
      call method cl_salv_table=>factory
        importing
          r_salv_table            = alv_report
        changing
          t_table                 = carrier_stack.
    catch cx_salv_msg.
      return.
    endtry.
    select *
      into table carrier_stack
      from scarr
             up to row_count rows.
    alv_report->display( ).
    call method excel_spreadsheet_manager=>copy_table_to_excel_worksheet
      exporting
        source_stack              = carrier_stack
        source_description        = 'Carriers'.
  endmethod.
endclass.
class booking_report                   definition
                                       abstract
                                       final.
  public section.
    class-methods: produce_report
                     importing
                       row_count
                         type data_exchangeable=>row_counter
                     raising
                       zcx_excel
                 .
endclass.
class booking_report                   implementation.
  method produce_report.
    data         : booking_stack  type standard table of sbook
                 , alv_report     type ref to cl_salv_table
                 .
    try.
      call method cl_salv_table=>factory
        importing
          r_salv_table            = alv_report
        changing
          t_table                 = booking_stack.
    catch cx_salv_msg.
      return.
    endtry.
    select *
      into table booking_stack
      from sbook
             up to row_count rows.
    alv_report->display( ).
    call method excel_spreadsheet_manager=>copy_table_to_excel_worksheet
      exporting
        source_stack              = booking_stack
        source_description        = 'Bookings'.
  endmethod.
endclass.
class process_driver                   definition
                                       abstract
                                       final.
  public section.
    class-methods: drive_process
                     importing
                       row_count
                         type data_exchangeable=>row_counter
                       recipient
                         type data_exchangeable=>email_recipient
                 .
endclass.
class process_driver                   implementation.
  method drive_process.
    try.
      call method flight_report=>produce_report exporting row_count = row_count.
      call method carrier_report=>produce_report exporting row_count = row_count.
      call method booking_report=>produce_report exporting row_count = row_count.
    catch zcx_excel ##NO_HANDLER.
    endtry.
    call method excel_spreadsheet_manager=>send_excel_via_email exporting recipient = recipient.
  endmethod.
endclass.
class email_address_resolver           definition
                                       abstract
                                       final.
  public section.
    class-methods: resolve_email_address
                     importing
                       userid
                         type syuname
                     exporting
                       email_address
                         type data_exchangeable=>email_recipient
                 .
endclass.
class email_address_resolver           implementation.
  method resolve_email_address.
    select single smtp_addr
      into email_address
      from adr6 ##WARN_OK
             inner join
           usr21 on usr21~persnumber eq adr6~persnumber
     where usr21~bname            eq userid.
  endmethod.
endclass.
  parameters     : rowcount       type data_exchangeable=>row_counter.
  parameters     : recipien       type data_exchangeable=>email_recipient.
initialization.
  call method email_address_resolver=>resolve_email_address
    exporting
      userid                      = sy-uname
    importing
      email_address               = recipien.
start-of-selection.
  call method process_driver=>drive_process
    exporting
      row_count                   = rowcount
      recipient                   = recipien.

Open your favorite ABAP editor, make a copy of this ABAP program and follow along as we apply changes to convert some of the static classes into classes that can be instantiated. For those who do not have ABAP2XLSX available at their site, replace class excel_spreadsheet_manager with the following source code:

class excel_spreadsheet_manager        definition
                                       abstract
                                       final.
  public section.
    class-methods: copy_table_to_excel_worksheet
                     importing
                       source_stack
                         type standard table
                       source_description
                         type string
                     raising
                       zcx_excel
                 , send_excel_via_email
                     importing
                       recipient
                         type data_exchangeable=>email_recipient
                 .
  private section.
    class-data   : excel          type string.
endclass.
class excel_spreadsheet_manager        implementation.
  method copy_table_to_excel_worksheet.
    data         : source_stack_lines type string.
    describe table source_stack lines source_stack_lines.
    concatenate excel
                source_stack_lines
                source_description
           into excel separated by space.
  endmethod.
  method send_excel_via_email.
    data         : message        type string.
    concatenate excel
                'would be sent to'
                recipient
           into message separated by space.
    message message type 'I'.
  endmethod.
endclass.

and include the following local exception class definition after the report statement:

class zcx_excel                        definition
                                       inheriting from cx_static_check.
endclass.

Motivation

Currently all the local classes we defined in our example program are static classes. Static classes offer ABAP programmers a stepping stone toward becoming more familiar with object-oriented principles due to their similarity with ABAP function groups, specifically:

  • Function groups and static classes both offer only a single copy of the attributes and data fields they define.
  • Function groups and static classes both are loaded into storage with the first reference to one of its members.
  • Methods of static classes can be invoked via the class name, similar to the way function modules can be invoked simply via the function module name.

Though static classes are easier to grasp for those new to OO concepts, they have limitations to what they can offer with a truly object-oriented design. Indeed, many object-oriented scholars frown on the definition and use of a static class since there is no object associated with it.

Changing the report classes to enable instantiation

Let’s start with the static classes flight_report, carrier_report and booking_report. Change these classes by doing the following:

  • Remove the qualifier abstract from their class definition statements.
  • Change the definition of their method produce_report from a static method to an instance method by replacing “class-methods” with “methods”.

A syntax check at this point will fail on the statement invoking method produce_report of class flight_report. Yes, this class no longer has a static method, so this statement invoking a static method is no longer applicable. To resolve this and the other imminent syntax errors, include the following statements at the top of method drive_process:

    data         : flight_report  type ref to flight_report
                 , carrier_report type ref to carrier_report
                 , booking_report type ref to booking_report
                 .
    create object: flight_report
                 , carrier_report
                 , booking_report
                 .

The data statements define instance reference variables to each of these classes. The create object statement creates instances of these three types of classes, placing the references to these instances into the respective instance references variables. In addition, change each of the call method statements in the subsequent try-endtry block so that method name produce_report is preceded not by a class selector (=>) but by an instance selector (->), as in:

  call method flight_report->produce_report exporting row_count = row_count.
  call method carrier_report->produce_report exporting row_count = row_count.
  call method booking_report->produce_report exporting row_count = row_count.

Now a syntax check will pass again. Executing the program at this point should prove that it still works as before.

What we’ve done here is to change the flight_report, carrier_report and booking_report classes from static classes to classes that can be instantiated. In addition, we’ve changed the drive_process method to a) create instances of these classes and then b) invoke the produce_report method upon those instances. Prior to these changes the program could not create instances of its local classes, but after applying these changes it can, meaning that we now have objects providing the reports to us.

Changing the excel_spreadsheet_manager class to enable instantiation

Next, we’ll do for local static class excel_spreadsheet_manager the same thing we just did for each of the local static report classes, but as you’ll soon see, this change is a bit more involved. Start by doing the following:

  • Remove the qualifier abstract from its class definition statement
  • Change the definition of its methods from static methods to instance methods by replacing “class-methods” with “methods”.
  • Change the definition of the private attribute excel from a static attribute to an instance attribute by replacing “class-data” with “data”.

A syntax check now will fail on the call to method copy_table_to_excel_worksheet in method produce_report of class flight_report. Since class excel_spreadsheet_manager no longer has static methods, these methods no longer can be invoked via the class name, but more to the point is that to invoke the methods of class excel_spreadsheet_manager we now need an instance reference to it. To facilitate this, change the signature for produce_report in class flight_report so that it now accepts a second importing parameter as a reference to an instance of excel_spreadsheet_manager, as in:

    methods      : produce_report
                     importing
                       row_count
                         type data_exchangeable=>row_counter
                       excel_spreadsheet_manager
                         type ref to excel_spreadsheet_manager
                     raising
                       zcx_excel
                 .

Then change method produce_report of class flight_report so that the call to method name copy_table_to_excel_worksheet is preceded not by a class selector (=>) but by an instance selector (->), as in:

call method excel_spreadsheet_manager->copy_table_to_excel_worksheet
  exporting
    source_stack              = flight_stack
    source_description        = 'Flights'.

Apply this same relative change to both classes carrier_report and booking_report. Afterward, change method drive_process to:

  • include a new reference variable to class excel_spreadsheet_manager
  • include this new reference variable on the create object statement
  • adjust all the calls to methods produce_report to include the now-mandatory second exporting parameter
  • change the call to method send_excel_via_email of class excel_spreadsheet_manager so that the call to this method is preceded not by a class selector (=>) but by an instance selector (->)

The code in method drive_process now should look like this:

  method drive_process.
    data         : flight_report  type ref to flight_report
                 , carrier_report type ref to carrier_report
                 , booking_report type ref to booking_report
                 , excel_spreadsheet_manager
                                  type ref to excel_spreadsheet_manager
                 .
    create object: flight_report
                 , carrier_report
                 , booking_report
                 , excel_spreadsheet_manager
                 .
    try.
      call method flight_report->produce_report exporting row_count = row_count
                                                          excel_spreadsheet_manager = excel_spreadsheet_manager.
      call method carrier_report->produce_report exporting row_count = row_count
                                                          excel_spreadsheet_manager = excel_spreadsheet_manager.
      call method booking_report->produce_report exporting row_count = row_count
                                                          excel_spreadsheet_manager = excel_spreadsheet_manager.
    catch zcx_excel ##NO_HANDLER.
    endtry.
    call method excel_spreadsheet_manager->send_excel_via_email exporting recipient = recipient.
  endmethod.

Now a syntax check will pass again. Executing the program at this point should prove that it still works as before.

What we’ve done here is to change class excel_spreadsheet_manager from a static class to an instance class, but just look at all the other changes this required:

  • We now create an instance of this class in method drive_process.
  • We now pass the reference to this instance on the signatures for the produce_report methods of classes flight_report, carrier_report and booking_report.
  • In the produce_report methods of classes flight_report, carrier_report and booking_report, we now invoke the method copy_table_to_excel_worksheet using the instance passed in through the signature of produce_report.
  • We now invoke method send_excel_via_email using the excel_spreadsheet_manager reference variable defined and populated in method drive_process.

Dependency Injection

One of the notable things about the changes we’ve made here is that the produce_report methods of classes flight_report, carrier_report and booking_report have had their signatures changed to accept a reference to an instance of a class on an importing parameter. In this case the instance is one of type reference to excel_spreadsheet_manager. When excel_spreadsheet_manager was defined as a static class its methods could be reached from anywhere within the program simply by prefixing the method calls with the class qualifier, as in:

  call method excel_spreadsheet_manager=>copy_table_to_excel_worksheet . . .

Notice the use of the class selector (=>) in the statement above instead of the instance selector (->) now being used for such calls. Now that excel_spreadsheet_manager is no longer a static class, the produce_report methods no longer would have had access to what is now an instance of this class. Accordingly, the produce_report methods of classes flight_report, carrier_report and booking_report need to have an instance of class excel_spreadsheet_manager made available to them. With our new process, the instance on which the produce_report method is dependent is injected into the method through its signature. This concept is known as dependency injection. There are other ways to inject dependencies into instances of classes, but when a method signature provides an object on which the method depends, it is known as parameter injection, a specific type of dependency injection. In short, dependency injection is in effect when a class or method is provided with a dependency it needs to satisfy its processing.

Summary

We’ve made enough changes for now and the final image of the code looks like this:

report.
interface data_exchangeable.
  types          : row_counter    type n length 02.
  types          : email_recipient
                                  type adr6-smtp_addr.
endinterface.
class excel_spreadsheet_manager        definition
                                       final.
  public section.
    methods      : copy_table_to_excel_worksheet
                     importing
                       source_stack
                         type standard table
                       source_description
                         type string
                     raising
                       zcx_excel
                 , send_excel_via_email
                     importing
                       recipient
                         type data_exchangeable=>email_recipient
                 .
  private section.
    data         : excel          type ref to zcl_excel.
endclass.
class excel_spreadsheet_manager        implementation.
  method copy_table_to_excel_worksheet.
    constants    : first_column   type char1     value 'A'
                 .
    data         : worksheet      type ref to zcl_excel_worksheet
                 , worksheet_title
                                  type zexcel_sheet_title
                 , table_settings type zexcel_s_table_settings
                 .
    table_settings-table_style    = zcl_excel_table=>builtinstyle_medium2.
    table_settings-show_row_stripes
                                  = abap_true.
    table_settings-nofilters      = abap_true.
    table_settings-top_left_column
                                  = first_column.
    table_settings-top_left_row   = 01.
    if excel is not bound.
      create object excel.
      worksheet                   = excel->get_active_worksheet( ).
    else.
      worksheet                   = excel->add_new_worksheet( ).
    endif.
    worksheet_title               = source_description.
    worksheet->set_title( worksheet_title ).
    worksheet->bind_table(
      ip_table                    = source_stack
      is_table_settings           = table_settings
      ).
  endmethod.
  method send_excel_via_email.
    constants    : excel_file_type
                                 type string value '.xlsx'
                 , file_name_parameter
                                  type string value '&SO_FILENAME='
                 .
    data         : excel_writer   type ref to zif_excel_writer
                 , excel_as_xstring
                                  type xstring
                 , excel_as_xstring_bytecount
                                  type i
                 , excel_as_solix_stack
                                  type solix_tab
                 , mail_send_request
                                  type ref to cl_bcs
                 , mail_message   type ref to cl_document_bcs
                 , any_bcs_exception
                                  type ref to cx_bcs
                 , diagnostic     type string
                 , mail_title     type so_obj_des
                 , mail_text_stack
                                  type soli_tab
                 , mail_text_entry
                                  like line
                                    of mail_text_stack
                 , mail_attachment_subject
                                  type sood-objdes
                 , mail_attachment_bytecount
                                  type sood-objlen
                 , mail_attachment_header_stack
                                  type soli_tab
                 , mail_attachment_header_entry
                                  like line of mail_attachment_header_stack
                 , internet_email_recipient
                                  type ref to if_recipient_bcs
                 , successful_send
                                  type abap_bool
                 , file_name      type string
                 .
    " Much of the code here was lifted from method send_mail of
    " class lcl_ouput, defined in object ZDEMO_EXCEL_OUTPUTOPT_INCL:
    concatenate sy-repid          " this report name
                sy-datum          " current date
                sy-uzeit          " current time
                excel_file_type   " excel file extension
           into file_name.
    mail_title                    = file_name.
    mail_attachment_subject       = file_name.
    mail_text_entry               = 'See attachment'.
    append mail_text_entry
        to mail_text_stack.
    concatenate file_name_parameter
                file_name
           into mail_attachment_header_entry.
    append mail_attachment_header_entry
        to mail_attachment_header_stack.
    create object excel_writer type zcl_excel_writer_2007.
    excel_as_xstring              = excel_writer->write_file( excel ).
    excel_as_solix_stack          = cl_bcs_convert=>xstring_to_solix( iv_xstring = excel_as_xstring ).
    excel_as_xstring_bytecount    = xstrlen( excel_as_xstring ).
    mail_attachment_bytecount     = excel_as_xstring_bytecount.
    try.
      mail_message                = cl_document_bcs=>create_document(
                                      i_type    = 'RAW' "#EC NOTEXT
                                      i_text    = mail_text_stack
                                      i_subject = mail_title
                                      ).
      mail_message->add_attachment(
        i_attachment_type         = 'XLS' "#EC NOTEXT
        i_attachment_subject      = mail_attachment_subject
        i_attachment_size         = mail_attachment_bytecount
        i_att_content_hex         = excel_as_solix_stack
        i_attachment_header       = mail_attachment_header_stack
        ).
      mail_send_request           = cl_bcs=>create_persistent( ).
      mail_send_request->set_document( mail_message ).
      internet_email_recipient    = cl_cam_address_bcs=>create_internet_address( recipient ).
      mail_send_request->add_recipient( internet_email_recipient ).
      successful_send             = mail_send_request->send( ).
      commit work.
      if successful_send eq abap_false.
        message i500(sbcoms) with recipient.
      else.
        message s022(so).
        message 'Document ready to be sent - Check SOST' type 'I'.
      endif.
    catch cx_bcs into any_bcs_exception.
      diagnostic                  = any_bcs_exception->if_message~get_text( ).
      message diagnostic type 'I'.
    endtry.
  endmethod.
endclass.
class flight_report                    definition
                                       final.
  public section.
    methods      : produce_report
                     importing
                       row_count
                         type data_exchangeable=>row_counter
                       excel_spreadsheet_manager
                         type ref to excel_spreadsheet_manager
                     raising
                       zcx_excel
                 .
endclass.
class flight_report                    implementation.
  method produce_report.
    data         : flight_stack   type standard table of sflight
                 , alv_report     type ref to cl_salv_table
                 .
    try.
      call method cl_salv_table=>factory
        importing
          r_salv_table            = alv_report
        changing
          t_table                 = flight_stack.
    catch cx_salv_msg.
      return.
    endtry.
    select *
      into table flight_stack
      from sflight
             up to row_count rows.
    alv_report->display( ).
    call method excel_spreadsheet_manager->copy_table_to_excel_worksheet
      exporting
        source_stack              = flight_stack
        source_description        = 'Flights'.
  endmethod.
endclass.
class carrier_report                   definition
                                       final.
  public section.
    methods      : produce_report
                     importing
                       row_count
                         type data_exchangeable=>row_counter
                       excel_spreadsheet_manager
                         type ref to excel_spreadsheet_manager
                     raising
                       zcx_excel
                 .
endclass.
class carrier_report                   implementation.
  method produce_report.
    data         : carrier_stack  type standard table of scarr
                 , alv_report     type ref to cl_salv_table
                 .
    try.
      call method cl_salv_table=>factory
        importing
          r_salv_table            = alv_report
        changing
          t_table                 = carrier_stack.
    catch cx_salv_msg.
      return.
    endtry.
    select *
      into table carrier_stack
      from scarr
             up to row_count rows.
    alv_report->display( ).
    call method excel_spreadsheet_manager->copy_table_to_excel_worksheet
      exporting
        source_stack              = carrier_stack
        source_description        = 'Carriers'.
  endmethod.
endclass.
class booking_report                   definition
                                       final.
  public section.
    methods      : produce_report
                     importing
                       row_count
                         type data_exchangeable=>row_counter
                       excel_spreadsheet_manager
                         type ref to excel_spreadsheet_manager
                     raising
                       zcx_excel
                 .
endclass.
class booking_report                   implementation.
  method produce_report.
    data         : booking_stack  type standard table of sbook
                 , alv_report     type ref to cl_salv_table
                 .
    try.
      call method cl_salv_table=>factory
        importing
          r_salv_table            = alv_report
        changing
          t_table                 = booking_stack.
    catch cx_salv_msg.
      return.
    endtry.
    select *
      into table booking_stack
      from sbook
             up to row_count rows.
    alv_report->display( ).
    call method excel_spreadsheet_manager->copy_table_to_excel_worksheet
      exporting
        source_stack              = booking_stack
        source_description        = 'Bookings'.
  endmethod.
endclass.
class process_driver                   definition
                                       abstract
                                       final.
  public section.
    class-methods: drive_process
                     importing
                       row_count
                         type data_exchangeable=>row_counter
                       recipient
                         type data_exchangeable=>email_recipient
                 .
endclass.
class process_driver                   implementation.
  method drive_process.
    data         : flight_report  type ref to flight_report
                 , carrier_report type ref to carrier_report
                 , booking_report type ref to booking_report
                 , excel_spreadsheet_manager
                                  type ref to excel_spreadsheet_manager
                 .
    create object: flight_report
                 , carrier_report
                 , booking_report
                 , excel_spreadsheet_manager
                 .
    try.
      call method flight_report->produce_report exporting row_count = row_count
                                                          excel_spreadsheet_manager = excel_spreadsheet_manager.
      call method carrier_report->produce_report exporting row_count = row_count
                                                          excel_spreadsheet_manager = excel_spreadsheet_manager.
      call method booking_report->produce_report exporting row_count = row_count
                                                          excel_spreadsheet_manager = excel_spreadsheet_manager.
    catch zcx_excel ##NO_HANDLER.
    endtry.
    call method excel_spreadsheet_manager->send_excel_via_email exporting recipient = recipient.
  endmethod.
endclass.
class email_address_resolver           definition
                                       abstract
                                       final.
  public section.
    class-methods: resolve_email_address
                     importing
                       userid
                         type syuname
                     exporting
                       email_address
                         type data_exchangeable=>email_recipient
                 .
endclass.
class email_address_resolver           implementation.
  method resolve_email_address.
    select single smtp_addr
      into email_address
      from adr6 ##WARN_OK
             inner join
           usr21 on usr21~persnumber eq adr6~persnumber
     where usr21~bname            eq userid.
  endmethod.
endclass.
  parameters     : rowcount       type data_exchangeable=>row_counter.
  parameters     : recipien       type data_exchangeable=>email_recipient.
initialization.
  call method email_address_resolver=>resolve_email_address
    exporting
      userid                      = sy-uname
    importing
      email_address               = recipien.
start-of-selection.
  call method process_driver=>drive_process
    exporting
      row_count                   = rowcount
      recipient                   = recipien.

We now have instances of local classes being created and we are passing instances between objects via dependency injection.

What’s next?

There remain other concepts of object-oriented programming for us to explore using this simple example program. Currently all the three report classes contain much duplicated code. The next step is to refactor the program so that these three report classes can inherit code common to all of them. This will be covered in the blog representing part 3 of this 6-part series Getting comfortable using the Object-Oriented design model with ABAP.

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12 Comments

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  1. Michelle Crapo

    Very nice examples and explanation.  I think we all still need this.  Yes, OOP has been around for awhile.   But guess what? Some of us don’t use it all the time.  Value, this is value added.

    I use it (OOP) for as much of my work as it makes sense to.   How do I determine if it makes sense?

    1.  How quick do I have to finish a project.
    2. Am I working with old code where it would take a lot of effort to rework and it hasn’t been touched for years.
    3. Sometimes I do the hybrid method.  <gasp> Both structural and OOP in the same program.

    You are doing a great job of showing how to do it.  But for the doubters – and maybe you did this in the first blog – I admit I haven’t gotten there yet.   Why to do it is always a nice add.  The answer that seems to be the norm is because you can no longer avoid it, and keep up with the new tools.  True.  But what about backend programming, you don’t need OOP for that yet.

    Maybe some of others will add comments about why OOP is such a good idea.  If not I’ll come back and add my reasons.   (Maybe, I’m struggling to find time to read blogs.)

    Anyway nice one!

    Michelle

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    1. Matthew Billingham

      OOPS is a good idea because it makes life much easier if you want to use the ABAP Unit Test framework.

      Static classes are bad, because (among other things) they get in the was of using ABAP Unit tests.

      ABAP Unit tests are a good idea because when you make a change to a program that has them, after your change you can tell quite quickly if you’ve managed to break something. (Assuming a comprehensive set of unit tests- where you don’t have that, you at least have confidence that you haven’t broken the areas that do have tests).

      ABAP Unit tests are a worthwhile investment because they reduce the cost of maintenance by reducing consequent errors when making changes.

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      1. Michelle Crapo

        😉 Perfectly said.  Of course many people are not doing unit tests yet.   Ummm….  That would be me!  I don’t use them consistently.  I’ll get there.  The whole “Don’t touch my data or die” seems to work for me.  I didn’t realize I was that scary.

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    2. Joao Sousa

      I think the rules are what you are following, the most important being time. If someone gives you 3 hours to create a quick ALV report you’re not going to structure your code that well, but that’s … life.

      I would just add one rule. Is this meant to be reusable? Everything should be, but in practice not everything will get the time investment.

      (2) 
    3. Paul Hardy

      Many years ago now I wrote a series og blogs about my journey from procedural to OO programming. I wanted to prove that OO programming was better for a concrete reason than the “its good because it is” or “you are forced to use it, so use it” arguments.

      Many years have gone by and I do everything OO now, I have become a convert. I even do “simple” ALV reports using a MVC template, as “simple” reports grow and mutate into monsters.

      I would recommend everyone to try and get their heads around what the SOLID principles really mean. I also warn that done wrongly, OO code can be horrifying, much worse than procedural. Done correctly, it is much better.

      The overarching argument is about maintainability. A program gets created and goes live – that is 1% of its life cycle. The other 99% is bug fixing and enhancements.

      Unit testing can massively reduce the rsik during that 99% phase, and to do proper unit testing you really need the code to be OO. Moreover, forcing yourself to write testable code forces the design of the program to be better by which i mean clearer and more maintainable.

      To use a money based analogy imagine you had two possible ways to pay your mortgage:-

      10,000 dollars the first month, 1 dollar a month for the next 30 years.

      1000 dollars every month for the next thirty years, plus every so often a huge monster comes around and beats the living daylights out of you.

      Put like that the choice is obvious. This is a very aprt analogy for programming because people say “well I don’t HAVE ten thousand dollars so I will have to take the second option” which comes out as “we have a very tight deadline, it does not need to be good, it just needs to work”.

      The end result – up until now – is everyone taking the second option. The monster is your boss and/or the end users when things break catastrophically every so often.

      One of my aims in life is to try and get people on the TDD / Unit Testing path. I do it for real – only proper TDD this year, I have done unit testing for ages – and I can tell you if you stick to your guns and force yourself to do it, but you will be a hundred times the programmer you were before.

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  2. Bärbel Winkler

    Thanks again, James!

    To recap: even if a program’s logic doesn’t really require instances of objects it’s better to just add the additional statements like the data-definitions for “TYPE REF TO” and CREATE OBJECTS and to subsequently call them as instance instead of class-methods?

    Cheers

    Baerbel

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  3. Chaouki AKIR

    Why,

    when the classes were statics you added the qualifier ‘ABSTRACT’ ?

    And

    when the classes become instantiable you omit the qualifier ‘ABSTRACT’ ?

     

    (1) 
    1. James E. McDonough Post author

      Chaouki,

      With ABAP, the qualifier ABSTRACT denotes a class that cannot be instantiated.  For static classes the qualifier ABSTRACT is optional, but In combination with the qualifier FINAL it clearly denotes a static class without requiring the developer to look any further to find the absence of instance members to indicate a static class.

      Jim

       

      (2) 

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