Structured COBOL programming

– The class definition is specified in COBOL with procedures and global data that looks like standard COBOL.. • A CLASS is a group of objects that share attributes which are methods f

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CHAPTER 18

AN INTRODUCTION TO OBJECT-ORIENTED

PROGRAMMING

Advantages of Object-Oriented Programming

• Object-oriented programming ( OOP ) is a concept that has the potential for

significantly enhancing the quality of all programs.

• This concept is considered by many to to

be the key to improved productivity in

future programs.

– ANSI formed an OO COBOL Task Group to

define the OO extensions to the COBOL

language as a part of the COBOL 2000+

standard.

Advantages of Object-Oriented Programming

• Some programming languages that

already implement the OO approach are:

– SMALLTALK

– C++

• Keep in mind that the concept of oriented programming will be added to the COBOL standard as an extension

object-– Thus any new compiler incorporating object

oriented techniques will be compatible with

Overview of Object-Oriented

Programming

• Data and procedures are combined and

stored in a program as units referred to as objects.

• Action occurs when an object receives a

message from the user.

• Services or actions are performed by the program as responses to user messages.

Overview of Object-Oriented

Programming

• Objects can be written so that they share

attributes data and methods with other objects.

– Objects can have any number of other

attributes unique to them.

– Data and procedure components need only be

written once and copied to all objects with

same attributes.

• A class defines a template for a series of similar objects.

– The class can be used to define and create

objects that are the same except for the value

of their data.

• By defining classes and objects within

classes the following takes place:

1 Complex applications will be easier to

develop.

2 Programs will become more standardized.

3 Reusable code stored in libraries will reduce duplication of effort, programming and

maintenance costs, and errors.

4 Improve programmer productivity

5 Objects can be acted on in any program by responding to the messages provided by the user.

• In summary:

– Data and procedures are combined into a

class definition.

– The class definition is specified in COBOL with

procedures and global data that looks like

standard COBOL.

– Multiple instances of a class, each with its

own local data, can be created at any point.

– These instances of a class are the objects that

can send and receive messages from other

objects.

• OOP is a different way of writing

programs.

• With traditional code, actions are

accomplished by procedures that act on

• Objects are ENCAPSULATED:

– This means their data and procedures are

hidden behind an INTERFACE

• One goal of OOP is to develop libraries of objects that can be shared and called into user programs as needed

– CALL and COPY are verbs that can achieve

some of the objectives of OOP

• A CLASS is a group of objects that share

attributes which are methods for

operating on the data.

– A METHOD is an action achieved by issuing a message to an object.

• A method is really an object’s way of responding to a message.

– Defining classes means placing reusable code

in a central location or library.

• An object is called an INSTANCE of a

class.

– Objects INHERIT attributes data and

procedures- from their class.

• A class can include a group of objects and may be included in another object called a

MEMBER object

Example-1:

• A Bank-Account may be defined as a

class

• It may have checking-account and

savings-account as subclasses, each of which shares data attributes (e.g.,

account number and balance) and

procedures (e.g., calculating interest)

Overview: Example-2

A Method that can be applied to these

classes include deposit and withdrawal

• All objects within bank-account can share deposit and withdrawal services

– That means that the mechanisms used for

withdrawing or depositing money will be the same for all objects within the class

• Each object can have additional methods not inherited from the class but unique to that object

– That is, process-check-fee can be a method

applied to checking-account but not to

savings-account.

Example-3

• Data such as account-number can be

shared by objects within the class as well

• This may be made available to users for

processing but may also be protected so that users can enter and retrieve them,

but not be able to change them.

• Classes and their objects consist of data and procedures.

• There are two types of data in a class:

INSTANCE VARIABLE object data and

procedures that are unique for each object in the class

FACTORY data and procedures that are data shared by all objects in the class Class is a COBOL reserved word so we use FACTORY.

• Factory data must be set to its initial value using the INITIALIZE verb or a VALUE clause (e.g., interest rate).

• METHODS can be two types:

– Object methods unique to each object in the class.

– Factory methods shared by all objects in the class.

• Objects are identified by unique names called OBJECT HANDLES

• POLYMORPHISM means a method can be implemented differently depending on the object.

– Withdrawal , for example, may be

• Although the term " polymorphism" itself may be new to you, it has relevance to the current COBOL language.

• The READ statement, for example is

polymorphic in that it results in different actions depending on whether we are

reading from a sequential, indexed, or

relative file.

• The Interface that links the Method to the object may be different but the service

provided will be similar.

– An INTERFACE is the entire set of messages

to which an object can respond along with

the parameters required by each message.

• The concept of DATA ABSTRACTION in

OOP encourages programmers to think of data and methods in abstract terms, as

fixed objects;

– Common objects data and

procedures should be factored out and located in

ancestor classes, sometimes referred to as

abstract classes.

• Consider the following analogies:

Terms and Concept Analogies

Object-Oriented Traditional

Terms Programming Terms

1 Methods 1 Procedures,

functions, subroutines

2 Instance variable 2 Data

3 Message 3 Procedure call or

function call

4 Class 4 Abstract data type

5 Inheritance 5 Copy

• ENCAPSULATION the ability to hide

internal details of data and procedures

while providing a public interface through

a user-defined message

• BASE CLASS a new class from an existing class through INHERITANCE

• A COBOL Example:

INVOKE ASAVINGSACCOUNT ‘Withdraw’

USING CUSTOMER-ACCT TRANS-AMT RETURNING ACCOUNT

– ASAVINGSACCOUNT may be an instance of

some class object such as ACCOUNT

• Often you begin establishing a new

instance of an object from a class of

• This may be accomplished by code such as:

INVOKE ASAVINGSACCOUNT 'New' RETURNING MYSTAVINGSACCOUNT.

• PERSISTENCE is the ability for changes to

be retained after the program is

terminated and when the program

executes it begins just as it ended.

– This is analogous to a "Save on EXIT" menu

item in some programs.

OBJECT-ORIENTED COBOL

PRODUCTS

• The following companies and products

have incorporated OO options into their COBOL compilers:

SOFTWARE DEVELOPER PRODUCT

Micro Focus Object COBOL

IBM Visual Age for COBOL Computer Associates Visual Realia COBOL Netron, Inc Netron/Fusion

TechBridge Technology TechBridge Builder

TUTORIAL FOR OO COBOL BY MICRO FOCUS

• Lesson One: "Hello World"

– Introduces the Class Browser , along with

some of the fundamental concepts of OO

COBOL programming

– In going through the tutorial, you'll learn:

• The basics parts of a class.

• The key elements needed to use an object.

• Passing a parameter to an object method.

• Passing a parameter to an object method and

TUTORIAL FOR OO COBOL BY MICRO FOCUS

• Lesson Two: "Hello World" and OO COBOL

– Permits working with an Object and a Class

• Throughout the rest of these lessons, you will find programs presented in pairs.

• Each pair consists of a drive program and a class program.

• Each pair is packaged as a project.

• Lesson Three: OOP and Parameter

Passing

– Permits the Passing of a Parameter to an

Object and Returning a Value.

WHAT YOU’VE LEARNED

• Once you've completed the tutorial

lessons outlined in your textbook you will have seen Personal COBOL’s basic

structures and had some amount of

interaction between program entities

• These are the basic components of all OO programming.

WHAT YOU’VE LEARNED

• You will have learned the following:

– How to open a project in the Browser and

view various program sections.

– How to compile and run a program.

– How important menu items work.

– How to work with a procedural COBOL

program in the Browser.

WHAT YOU’VE LEARNED

– The object-oriented syntax items in Personal

COBOL.

– The basic structure of classes and their

objects and how to access them with driver programs.

– Passing a parameter to an object method and

returning a value.

– How one object method can access a peer

method.

WHAT YOU’VE LEARNED

• What you didn't experience are the

concepts of inheritance and

polymorphism

• The Help/Online Tutorials and Reference Beginning Tutorials treats both of these in

a series of examples