Object Oriented ABAP

*&-------------------------------------------------------------------*
REPORT Z_PERSISTENT_GUID.
selection-screen begin of block b1 with frame title tit1.
parameters: sno like zstudent02-sno,
sname like zstudent02-sname,
mark1 like zstudent02-mark1,
mark2 like zstudent02-mark2,
guid like zstudent02-guid.
selection-screen end of block b1.
selection-screen begin of block b2 with frame title tit2.
parameters: r1 radiobutton group rad1,
r2 radiobutton group rad1,
r3 radiobutton group rad1.
selection-screen end of block b2.
data: agent type ref to zca_persist_02,
students type ref to zcl_persist_02.
data: result1 type ref to object,
result2 type ref to zcl_persist_02.
*-------------------------------------------------------------------*
* Load-of-Program
*-------------------------------------------------------------------*
load-of-program.
tit1 = text-001.
tit2 = tit1.
*-------------------------------------------------------------------*
* At Selection Screen
*-------------------------------------------------------------------*
at selection-screen.
if ( r2 eq 'X' ).
if sno is initial or sname is initial.
MESSAGE 'Enter the values in Sno/Sname fields'
TYPE 'E' DISPLAY LIKE 'E'.
endif.
endif.
*-------------------------------------------------------------------*
* Start-of-Selection
*-------------------------------------------------------------------*
start-of-selection.
agent = zca_persist_02=>agent.
if r1 eq 'X'.
TRY.
CALL METHOD AGENT->IF_OS_CA_PERSISTENCY~GET_PERSISTENT_BY_OID
EXPORTING
I_OID = guid
RECEIVING
RESULT = result1.
result2 ?= result1.
sno = result2->get_sno( ).
sname = result2->get_sname( ).
mark1 = result2->get_mark1( ).
mark2 = result2->get_mark2( ).
write:/ sno,