1. Simple class
This example shows how to create a simple employee class. The constructor method is used to initialize number and name of thje employee when the object is created. A display_employee method can be called to show the attributes of the employee, and CLASS-METHOD dosplay_no_of_employees can be called to show the total number of employees (Number of instances of the employee class).
REPORT zbc404_hf_events_1.
*********************************************************************
* L C L _ E M P L O Y E E
*********************************************************************
*—- LCL Employee – Definition
CLASS lcl_employee DEFINITION.
PUBLIC SECTION.
*——————————————————————–
* The public section is accesible from outside
*——————————————————————–
TYPES:
BEGIN OF t_employee,
no TYPE i,
name TYPE string,
END OF t_employee.
METHODS:
constructor
IMPORTING im_employee_no TYPE i
im_employee_name TYPE string,
display_employee.
* Class methods are global for all instances
CLASS-METHODS: display_no_of_employees.
PROTECTED SECTION.
*——————————————————————–
* The protecetd section is accesible from the class and its subclasses
*——————————————————————–
* Class data are global for all instances
CLASS-DATA: g_no_of_employees TYPE i.
PRIVATE SECTION.
*——————————————————————–
* The private section is only accesible from within the classs
*——————————————————————–
DATA: g_employee TYPE t_employee.
ENDCLASS.
*— LCL Employee – Implementation
CLASS lcl_employee IMPLEMENTATION.
METHOD constructor.
g_employee-no = im_employee_no.
g_employee-name = im_employee_name.
g_no_of_employees = g_no_of_employees + 1.
ENDMETHOD.
METHOD display_employee.
WRITE:/ ‘Employee’, g_employee-no, g_employee-name.
ENDMETHOD.
METHOD display_no_of_employees.
WRITE: / ‘Number of employees is:’, g_no_of_employees.
ENDMETHOD.
ENDCLASS.
************************************************************************
* R E P O R T
*********************************************************************
DATA: g_employee1 TYPE REF TO lcl_employee,
g_employee2 TYPE REF TO lcl_employee.
START-OF-SELECTION.
CREATE OBJECT g_employee1
EXPORTING im_employee_no = 1
im_employee_name = ‘John Jones’.
CREATE OBJECT g_employee2
EXPORTING im_employee_no = 2
im_employee_name = ‘Sally Summer’.
CALL METHOD g_employee1->display_employee.
CALL METHOD g_employee2->display_employee.
CALL METHOD g_employee2->display_no_of_employees.
2. Inheritance and polymorphism
This example uses a superclass lcl_company_employees and two subclasses lcl_bluecollar_employee and lcl_whitecollar_employee to add employees to a list and then display a list of employees and there wages. The wages are calcukated in the method add_employee, but as the wages are calculated differently for blue collar employees and white collar emplyees, the superclass method add_employee is redeifined in the subclasses.
Principles:
Create super class LCL_CompanyEmployees.
The class has the methods:
Constructor
Add_Employee – Adds a new employee to the list of employees
Display_Employee_List – Displays all employees and there wage
Display_no_of_employees – Displays total number of employees
Note the use of CLASS-DATA to keep the list of employees and number of employees the same from instance to instance.
Create subclasses lcl_bluecollar_employee and lcl_whitecollar_employee. The calsses are identical, except for the redifinition of the add_employee method, where the caclculation of wage is different.
Methodes:
Constructor. The constructor is used to initialize the attributes of the employee. Note that the constructor in the supclasss has to be called from within the constructor of the subclass.
Add_Employee. This is a redinition of the same method in the superclass. In the redefined class the wage is calcuated, and the superclass method is called to add the employees to the emploee list.:
The program
REPORT zbc404_hf_events_2 .
*******************************************************
* Super class LCL_CompanyEmployees
*******************************************************
CLASS lcl_company_employees DEFINITION.
PUBLIC SECTION.
TYPES:
BEGIN OF t_employee,
no TYPE i,
name TYPE string,
wage TYPE i,
END OF t_employee.
METHODS:
constructor,
add_employee
IMPORTING im_no TYPE i
im_name TYPE string
im_wage TYPE i,
display_employee_list,
display_no_of_employees.
PRIVATE SECTION.
CLASS-DATA: i_employee_list TYPE TABLE OF t_employee,
no_of_employees TYPE i.
ENDCLASS.
*– CLASS LCL_CompanyEmployees IMPLEMENTATION
CLASS lcl_company_employees IMPLEMENTATION.
METHOD constructor.
no_of_employees = no_of_employees + 1.
ENDMETHOD.
METHOD add_employee.
* Adds a new employee to the list of employees
DATA: l_employee TYPE t_employee.
l_employee-no = im_no.
l_employee-name = im_name.
l_employee-wage = im_wage.
APPEND l_employee TO i_employee_list.
ENDMETHOD.
METHOD display_employee_list.
* Displays all employees and there wage
DATA: l_employee TYPE t_employee.
WRITE: / ‘List of Employees’.
LOOP AT i_employee_list INTO l_employee.
WRITE: / l_employee-no, l_employee-name, l_employee-wage.
ENDLOOP.
ENDMETHOD.
METHOD display_no_of_employees.
* Displays total number of employees
SKIP 3.
WRITE: / ‘Total number of employees:’, no_of_employees.
ENDMETHOD.
ENDCLASS.
*******************************************************
* Sub class LCL_BlueCollar_Employee
*******************************************************
CLASS lcl_bluecollar_employee DEFINITION
INHERITING FROM lcl_company_employees.
PUBLIC SECTION.
METHODS:
constructor
IMPORTING im_no TYPE i
im_name TYPE string
im_hours TYPE i
im_hourly_payment TYPE i,
add_employee REDEFINITION.
PRIVATE SECTION.
DATA:no TYPE i,
name TYPE string,
hours TYPE i,
hourly_payment TYPE i.
ENDCLASS.
*—- CLASS LCL_BlueCollar_Employee IMPLEMENTATION
CLASS lcl_bluecollar_employee IMPLEMENTATION.
METHOD constructor.
* The superclass constructor method must be called from the subclass
* constructor method
CALL METHOD super->constructor.
no = im_no.
name = im_name.
hours = im_hours.
hourly_payment = im_hourly_payment.
ENDMETHOD.
METHOD add_employee.
* Calculate wage an call the superclass method add_employee to add
* the employee to the employee list
DATA: l_wage TYPE i.
l_wage = hours * hourly_payment.
CALL METHOD super->add_employee
EXPORTING im_no = no
im_name = name
im_wage = l_wage.
ENDMETHOD.
ENDCLASS.
*******************************************************
* Sub class LCL_WhiteCollar_Employee
*******************************************************
CLASS lcl_whitecollar_employee DEFINITION
INHERITING FROM lcl_company_employees.
PUBLIC SECTION.
METHODS:
constructor
IMPORTING im_no TYPE i
im_name TYPE string
im_monthly_salary TYPE i
im_monthly_deductions TYPE i,
add_employee REDEFINITION.
PRIVATE SECTION.
DATA:
no TYPE i,
name TYPE string,
monthly_salary TYPE i,
monthly_deductions TYPE i.
ENDCLASS.
*—- CLASS LCL_WhiteCollar_Employee IMPLEMENTATION
CLASS lcl_whitecollar_employee IMPLEMENTATION.
METHOD constructor.
* The superclass constructor method must be called from the subclass
* constructor method
CALL METHOD super->constructor.
no = im_no.
name = im_name.
monthly_salary = im_monthly_salary.
monthly_deductions = im_monthly_deductions.
ENDMETHOD.
METHOD add_employee.
* Calculate wage an call the superclass method add_employee to add
* the employee to the employee list
DATA: l_wage TYPE i.
l_wage = monthly_salary – monthly_deductions.
CALL METHOD super->add_employee
EXPORTING im_no = no
im_name = name
im_wage = l_wage.
ENDMETHOD.
ENDCLASS.
*******************************************************
* R E P O R T
*******************************************************
DATA:
* Object references
o_bluecollar_employee1 TYPE REF TO lcl_bluecollar_employee,
o_whitecollar_employee1 TYPE REF TO lcl_whitecollar_employee.
START-OF-SELECTION.
* Create bluecollar employee obeject
CREATE OBJECT o_bluecollar_employee1
EXPORTING im_no = 1
im_name = ‘Gylle Karen’
im_hours = 38
im_hourly_payment = 75.
* Add bluecollar employee to employee list
CALL METHOD o_bluecollar_employee1->add_employee
EXPORTING im_no = 1
im_name = ‘Gylle Karen’
im_wage = 0.
* Create whitecollar employee obeject
CREATE OBJECT o_whitecollar_employee1
EXPORTING im_no = 2
im_name = ‘John Dickens’
im_monthly_salary = 10000
im_monthly_deductions = 2500.
* Add bluecollar employee to employee list
CALL METHOD o_whitecollar_employee1->add_employee
EXPORTING im_no = 1
im_name = ‘Karen Johnson’
im_wage = 0.
* Display employee list and number of employees. Note that the result
* will be the same when called from o_whitecollar_employee1 or
* o_bluecolarcollar_employee1, because the methods are defined
* as static (CLASS-METHODS)
CALL METHOD o_whitecollar_employee1->display_employee_list.
CALL METHOD o_whitecollar_employee1->display_no_of_employees.
The resulting report
List of Employees
1 Karen Johnson 2.850
2 John Dickens 7.500
Total number of employees: 2