ABAP(Advanced Business Application Programming) is an object-oriented programming language that supports many oops concepts like other programming languages. It supports all the four pillars of oops i.e. Inheritance, Polymorphism, Abstraction, and Encapsulation. The interface is one of the oops concepts that ABAP supports and it plays a very important role in implementing all these oops concepts.

What is Interface in SAP ABAP

The interface in SAP ABAP is different from the class, it can not have any implementation like the class. It defines a set of method declarations that a class must implement without providing any implementation detail of that method. Interface helps in achieving multiple inheritance. Multiple inheritance can be defined as a class can inherit multiple interfaces. Due to Inheritance interface provides a base for polymorphism because the method declared in the interface behaves differently in different classes. Like class Interface can be defined locally or globally in the ABAP programming language.

Syntax for Creating an Interface in SAP ABAP

Syntax

INTERFACE interface-name
DATA declaration.....
ABSTRACT METHOD declaration.....
EVENT declaration....
.
.
ENDINTERFACE

Syntax of interface explained: Here INTERFACE is a keyword for declaring interface and interface-name is the name of interface. DATA declaration is declaring the data. METHOD declaration is declaring the method .It is important to note that all the methods declared in interface are Abstract. You can also declare many field like EVENT, CONSTANT etc. At the end of interface we declare ENDINTERFACE.

Implementation of Interface Inside Class in SAP ABAP

INTERFACE interface_name

Explanation: First we create a class inside that we use above syntax to implement interface. here interface_name means name of interface.

Implementing method of an interface inside class in SAP ABAP

METHOD interface_name~interface_method_name
satements
ENDMETHOD

Explanation: we use METHOD keyword to implement method of interface inside implementing class, interface_name~interface_method_name refers to the name of interface along with method name declare in interface.

Example Program

Here is an example of interface and a class implementing that interface.

* Creating interface
INTERFACE my_interface1
* declaring data variable
DATA: num1 TYPE i,
            num2 TYPE i,
            res TYPE i.
* Declaring abstract methods
METHOD : add.
METHOD: subtract.
ENDINTERFACE
* Creating class
CLASS my_class1 DEFINATION.
* Declaring public section because interface can implement only in the public section
public SECTION.
* Using interface inside class and assigning value of data attributes of interface
INTERFACEs my_interface1 DATA VALUES num1 = 5 , num2= 10.
ENDCLASS
* Class implementing Interface
CLASS my_class1 IMPLEMENTATION.
* Using method inside implementing class
METHOD my_interface1~add.
* adding two number
my_interface1~res =my_interface1~ num1 + my_interface1~num2.
* printing result
write: my_interface1~res.
ENDMETHOD 
METHOD my_interface1~subtract.
* subtracting two number
my_interface1~res =my_interface1~ num2 - my_interface1~num1.
* printing result
write:  my_interface1~res.
ENDMETHOD 
ENDCLASS.

Output

15
10

Program Execution – Creating Objects ‘object1’ and ‘object2’

Creating object 1 and calling add method

*creating object
start-OF-SELECTION.
data : object1  TYPE REF TO my_class1.
create OBJECT object1.
WRITE : 'Addition of given number is'.
call METHOD object1->my_interface1~add.

Output

Addition of given number is  15

Here we have created an object object1 of class my_class1 and call the add method of interface my_interface1 implemented in my_class1. After calling the output will be 15.

Creating object2 and calling subtract method

*creating object2
start-OF-SELECTION.
data : object2  TYPE REF TO my_class1.
create OBJECT object2.
WRITE : 'Subtraction of given number is'.
call METHOD object1->my_interface1~subtract.

Output

Subtraction of given number is  10

Here we have created an object object2 of class my_class1 and call the subtract method of interface my_interface1 implemented in my_class1. After calling the output will be 10.

Benefits and Application of Interface in SAP ABAP

• Same Method but Different Functionality: The method declare in interface can have different functionality when use in different class this is because we can not implement method in interface we can only declare that method. class implement or use that function according to their need. It also group common functionality which makes a program more readable.
• Multiple Inheritance: Inheritance support multiple inheritance, which means two or more class have same methods name but different functionality. A class can implement multiple interfaces, inherit the method declare in the interface whereas a class support only single inheritance.
• Polymorphism: It is a concept of oops, polymorphism is derived from a geek word poly means many and morph means form. The main purpose of inheritance is to achieve run time polymorphism. Inheritance provide a base for polymorphism as a single method declare in interface can be used by different class with different functionality.