Type pool and field symbols

Type pools (or type group)

*Define*

type-pool hktst.
TYPES: BEGIN of hktst_typ1,
		col1(10) TYPE c,
		col2 TYPE i,
       END OF hktst_typ1.

TYPES hktst_typ2 TYPE p DECIMALS 2.
CONSTANTS hktst_eleven TYPE i VALUE 11.

*Use Type pool definition*

TYPE-POOLS hktst.

DATA: dat1 type hktst_typ1,
      dat2 type hktst_typ2 VALUE '1.23',

WRITE: dat2, /hktst_eleven.

ABAP contains the following kinds of named data objects- 
text Symbols
variables
constants
Interface work areas

Ways of declaring variables in ABAP program

DATA: To declare variables whose lifetime is linked to the 
context of declaration

STATICS: To declare variables with static validity in procedures

CLASS-DATA - To declare static variables within classes

PARAMETERS: To declare elementary data objects that are also 
linked to an input field on a selection screen

SELECT-OPTIONS: To declare an internal table that is also linked 
to input fields on a selection screen

RANGES: To declare an internal table with the same structure as 
in SELECT-OPTIONS, but without linking it to a selection screen

DATA: BEGIN OF ADDRESS,
	FIRSTNAME(20) VALUE 'Fred',
	SURNAME(20) VALUE 'Flintstone',
	INITIALS(4) VALUE 'FF',
	STREET (20) VALUE 'Cave Avenue',
	NUMBER TYPE I VALUE '11',
	POSTCODE TYPE N VALUE '98765',
	CITY(20) VALUE 'Bedrock',
      END OF ADDRESS.

DATA: BEGIN OF NAME,
	SURNAME(20),
	FIRSTNAME(20),
	INITIALS(4),
	TITLE(10) VALUE 'Mister',
	END OF NAME.

MOVE-CORRESPONDING ADDRESS TO NAME

WRITE: / NAME-SURNAME,
	 NAME-FIRSTNAME,
	 NAME-INITIALS,
	 NAME-TITLE.

Fiels Symbols

These are placeholders or symbolic names of other fields.
These point to field contents and do not reserve their own memory


Fully Specified Field Symbols - 

DATA: BEGIN OF LINE,
	COL1,
	COL2 VALUE 'X',
	END OF LINE.

FIELD-SYMBOLS <FS> LIKE LINE.

ASSIGN LINE TO <FS>.

MOVE <FS>-COL2 TO <FS>-COL1.

WRITE COL1.

Output is X

____________________________________________________

Attaching a structure to a field symbol

DATA: WA(10) VALUE '0123456789'.

DATA: BEGIN OF LINE1,
	COL1(3),
	COL2(2),
	COL3(5),
      END OF LINE1.

DATA: BEGIN OF LINE2,
	COL1(2),
	COL2 LIKE SY-DATUM,
	END OF LINE2.

FIELD-SYMBOLS: <FS1> STRUCTURE LINE1 DEFAULT WA,
	       <FS2> STRUCTURE LINE2 DEFAULT WA.

ASSIGN LINE1 TO <FS1>.
ASSIGN LINE2 TO <FS2>.

WRITE: / <F1>-COL1, <F1>-COL2, <F1>-COL3,
       / <F2>-COL1, <F2>-COL2.

Output:

012 34 56789
01 2345/67/89