Difference between class and interface in ABAP Objects

Class and interface are interrelated, an interface cannot be implemented without a class
.interface do not have instances. Interface can be implemented in a class using the
statement INTERFACES <interface_name> in the public section of a class. The component of the interface are added automatically in the public section of the class. Now the question comes how do we access the components of the interface ?? Well the components of an interface can be identified as if they are components of the class, through the identifier <interface_name~interface _component >

Code:



Lets take an example.
INTERFACE my_interface .
METHODS my_interface_method exporting num type i.
ENDINTERFACE.
CLASS interface_class DEFINITION.
INTERFACES my_interface.
ENDCLASS.

CLASS interface_class IMPLEMENTATION.
METHOD my_interface~my_interface_method.
Write:/ num.
ENDMETHOD.
ENDCLASS.

The class must implement the methods of all interfaces implemented in it. The
implementation part of the class must contain a method implementation for each interface
method <imeth>:
METHOD <intf~imeth>.
...
ENDMETHOD.


Note:
Interfaces can be implemented by different classes. Each of these classes is extended by the same set of components. However, the methods of the interface can be implemented differently in each class.

Code:


INTERFACE common_interface.
METHODS: interface_method.
ENDINTERFACE.

CLASS interface_class1 DEFINITION.
PUBLIC SECTION.
INTERFACES common_interface.
ENDCLASS.

CLASS interface_class1 IMPLEMENTATION.
METHOD common_interface~interface_method. “interface method is implemented as type
1
WRITE:/ ‘ METHODS IMPLEMENTATION TYPE 1
ENDMETHOD.
ENDCLASS.

CLASS interface_class2 DEFINITION.
PUBLIC SECTION.
INTERFACES common_interface.
ENDCLASS.

CLASS interface_class2 IMPLEMENTATION.
METHOD common_interface~interface_method. “Interface method is implemented astype2
WRITE:/ ‘ METHODS IMPLEMENTATION TYPE 2
ENDMETHOD.
ENDCLASS