How to create a instance for the method

Question

it is showing me dump error for the call method
data: i_tab type /SCMB/DM_ORDER_TAB,
      grid1  TYPE REF TO /SCA/CL_SVORDER .
CALL METHOD grid1->READ_BY_IDS
  EXPORTING
   IS_CTRL      =
    IV_ORTYPE    = gt_po_detl-ortype
   IV_LOCKFLG   = /SCMB/CL_C_ORDER=>GC_FALSE
   IV_NOADDRESS = /SCMB/CL_C_ORDER=>GC_FALSE
   IV_MAPID     = /SCMB/CL_C_ORDER=>GC_FALSE
   IV_DUEQUAN   = /SCMB/CL_C_ORDER=>GC_FALSE
    IT_ORDERID   = itab_orderid
  IMPORTING
    ET_ORDERS    = i_tab
   ET_PROT      =
u r attempting to use a null object reference access a component (variable 'GRID!")
an object reference must point to an object (an instance of  a class ) before it can be used to acess a component either the reference was never set or it was set to null using the clear statement

Answer 1

sridhar loganathan,
A ABAP Class is just a definition of fields/variables called attributes and routines (like in standard ABAP forms and functions) called methods. Also you can have events, don't care about before necessary.
The definition itself is just a blueprint. Nothing exists, nothing can be used before you create an instance for this definition.
DATA: grid1 TYPE REF TO /SCA/CL_SVORDER creates a 'handler' for ( to be created) instances of the class.
The statement CREATE OBJECT grid1 creates an instance of the class as defined in the 'blueprint' and assigns the reference to this instance (with all methods, attributes and events) to reference field grid1.
In 999 of 1000 cases SAP creates just one object of a class. In those cases the definition of classes and uses of object oriented programming is more or less obsolete.
Anyway: Just keep in mind that you can not uses attributes and methods of the class directly (blueprint!) but only of the instance created.
An Exception to be noted are so-called Static attributes and methods where an instance is not required. Example ABAP_CHAR_UTILITIES=>HORIZONTAL_TAB gives the character for horizontal tab regardless of platform and char encoding (unicode!). Class ABAP_CHAR_UTILITIES defines static attribute HORIZONTAL_TAB - no instances necessary because this will never change in a given system.
Hope this sheds some light on it
Regards,
Clemens