IF_GRRM_API_CLUSTER is a standard SAP interface, see below for any documentation including details of methods, attributes, events etc. Interfaces are defined much the same as a class using the same transactions but act a bit like a template (in none OO terms). For example, a class would implement the interface and then inherit all of the methods etc from it. This provides a mechanism for unrelated objects to use a set of common behaviours and functionality.
You may have seen this already without knowing what it was, within SAP have you ever seen the method name prefixed by the name of an interface such as IF_GRRM_API_CLUSTER~METHOD_NAME . This means that the class has implemented an interface and that this method has been inherited from it.
For further relevant information about this interface enter IF_GRRM_API_CLUSTER into the relevant SAP transactions such as SE24, SE80. Also see the Resource section below to view other useful tips, screenshots, links and general information related to this SAP interface and its methods. Or even add your own for future reference
A method is a coding block that performs a certain procedure (i.e. ABAP functionality) on an object within the overall SAP class. In simple terms if the object is an SAP database table a method could be the procedure to add a record or to delete a record. If you are new to OO in many respects, the implementation of a method is similar to a function module and can be called in a very similar way using CALL METHOD.
Instead of "CALL FUNCTION", Methods are referenced using the following syntax: CALL METHOD CL_ABAP_CHAR_UTILITIES=>methodname EXPORTING/IMPORTING...
List of attributes within class IF_GRRM_API_CLUSTER. These can be referenced using the following syntax IF_GRRM_API_CLUSTER=>
Events are created within your class using special event handler methods. These must be registered at runtime for the event and can then be triggered using the ABAP syntax: RAISE EVENT