OpenEdge Getting Started:<br />Object-oriented Programming Summary comparison of classes and procedures

Table 5–1 compares the application implemented by the sample classes (see the "Sample classes" section) with the equivalent application implemented by comparative procedures (see the "Comparative procedures" section). The code numbers in the table match the commented numbers in the code for both classes and procedures.

Table 5–1: Comparing sample classes to comparative procedures
Code No.	Sample classes	Comparative procedures
1	The `acme.myObjs.CustObj` class inherits from `acme.myObjs.Common.CommonObj`.	`CustProc.p` defines a handle variable and runs `CommonProc.p` persistently, setting the handle. `CustProc.p` then uses `ADD-SUPER-PROCEDURE( )` to define `CommonProc.p` as a super procedure for it.
2	All the setup for `acme.myObjs.CustObj` takes place in the constructor.	All the setup for `CustProc.p` takes place in the main block of the procedure.
3	To establish an object reference to `acme.myObjs.Common.ErrorObj`, the method `ErrorHandler( )` is invoked inside the `acme.myObjs.CustObj` class. It is found in the super class and returns an instance of `acme.myObjs.Common.ErrorObj`.	To establish a handle to `ErrorProc.p`, the `ErrorHandler` user-defined function, which returns a handle to `ErrorProc.p` is first defined as a prototype `IN` `SUPER`. The function is defined in the super procedure, `CommonProc.p`. It is later invoked `CustProc.p` and returns a handle to `ErrorProc.p`.
4	In `ListDate( )` called on `acme.myObjs.Common.HelperClass` (through `Main`), when `updateTimestamp( )` is invoked on `acme.myObjs.CustObj`, it is found in its super class, `acme.myObjs.Common.CommonObj`.	In `Main.p`, when `updateTimestamp` is called in `CustProc.p`, it is found in its super procedure, `CommonProc.p`.
5	The `updateTimestamp( )` method initializes the value of the `timestamp` data member in `acme.myObjs.Common.CommonObj`. Because it is an inherited data member, it can be referenced in `acme.myObjs.CustObj`.	The `updateTimestamp` procedure in `CommonProc.p` initializes the value of the `SHARED` variable, `timestamp`. In order for `CustProc.p` to use `timestamp`, it must define it as `NEW` `SHARED`.
6	When `acme.myObjs.CustObj` is deleted, the destructor automatically runs and cleans up program resources.	Before deleting the procedure object, the internal procedure `CleanUp` is called in `Main.p` to clean up resources.
7	The `acme.myObjs.NECustomer` class inherits from `acme.myObjs.CustObj`.	`NECustomer.p` must go through the same process to add `CustProc.p` as a super procedure, as did `CustProc.p` to add `CommonProc.p` as a super procedure, described earlier.
8	The constructor for `acme.myObjs.NECustomer` invokes the constructor for `acme.myObjs.CustObj`. If it had parameters to pass (which it does not in this case), it would do that here.	If `CustProc.p` took parameters (which it does not in this case) then `NECustomer.p` would have to pass them when `CustProc.p` is run.
9	`acme.myObjs.NECustomer` overrides the `GetCustomerName( )` method in `acme.myObjs.CustObj`. The override uses the `SUPER` system reference to invoke the super class implementation of this method.	`NECustomer.p` defines a separate version of the `GetCustomerName` internal procedure defined in the super procedure `CustProc.p`. The `NECustomer.p` version uses the `RUN` `SUPER` statement to invoke the super procedure implementation of this internal procedure.