Object COBOL Concepts

Chapter 1: Introduction to Object COBOL

Object COBOL extends Micro Focus technology to enable object-oriented (OO) programming in COBOL, while retaining all the dialects and features previously available. This chapter explains:

• The new features added to COBOL to enable OO programming
  
  
• How to use this manual to begin programming with Object COBOL
  
  
• Where to learn more about OO

If you don't want to create OO programs you don't need to read this manual, and can use Micro Focus Object COBOL in the same way you used Micro Focus COBOL.

1.1 OO Features of Object COBOL

To enable you to write OO programs in COBOL, MERANT has added the following components and features to the COBOL system:

• Compiler support for new COBOL syntax for OO programming.

  Object COBOL has a small amount of new syntax - one new verb (INVOKE), one new data type (OBJECT REFERENCE) and three new types of header paragraph
  
  

• An Object COBOL run-time system.

  Adds support for creation of objects, dynamic message binding, and inheritance to the COBOL run-time system
  
  

• An Object COBOL class library.

  A library of pre-defined objects which you can use as a foundation for building your own applications

1.2 Getting Started with Object COBOL

This book is intended to help you get started programming with Object COBOL as quickly as possible. However, if you are completely new to OO programming you might want to do some background reading to familiarize yourself with the new concepts, and perhaps get some training in Object-Oriented Analysis and Design. There is a list of books in the section Reading List.

The next two sections explain:

• How you develop OO applications with Object COBOL.
  
  
• How to use this manual and the other documentation to get started quickly.

1.2.1 Developing OO Applications

The list below shows the basic steps to develop an OO application.

To develop an OO application:

1. Analyze the problem, and identify the objects needed to solve it.
   
   
2. Identify the relationships between the objects.

   You need to see where inheritance hierarchies will help you to reuse code, and to see which objects will interact with each other and with the messages they will send.

3. Find which classes you already have which you can reuse. Some of these will come from the Class Library, while others might have been written either by you or by someone else in your organization. Use the Class Library documentation to find out what is already there.
   
   
4. Start coding your application.

   You can use any text editor to code Object COBOL; we recommend the Micro Focus Editor. Alternatively, you can develop and debug your application on NetExpress, and transfer the code to a UNIX platform for production. Object COBOL code is portable between NetExpress and UNIX, except for code developed for:

   • GUI programming
     
     
   • COM and OLE automation

   which are not supported on UNIX.

5. Compile your application.
   
   
6. Debug your application using Animator.
   
   
7. Repeat steps 4 through 6 until you are ready to ship your application to end-users.
   
   
8. Compile and link your application, ready for shipping.

Steps 1 and 2 are OO analysis, and fall outside of the scope of this book. Some information sources to help you get started are provided in the section Learning More About Object-Orientation. The next section explains how you can use the documentation to help you with steps 3 to 8.

1.2.2 Using the Documentation

When you start developing OO applications with Object COBOL, you learn about three things:

• Object COBOL OO syntax and object model.

  How OO is handled by Object COBOL. There is very little new syntax to learn.

• The OO development environment.

  The development environment for OO will be familiar to any previous users of Micro Focus COBOL.

• The Object COBOL Class Library.

  The Class Library gives you a set of ready-made objects which you can use in your applications. The tutorials in this book give you an introduction to the main types of classes in the Class Library, so that you can get a feel for what is in there. You don't have to know the entire Class Library to begin programming.

This manual is divided into parts for ease of use:

• Part 1: Introduction

  Consists of this chapter and the chapter Object COBOL Concepts. Read the Object COBOL Concepts chapter to get a quick overview of the key points about OO programming and Object COBOL.

• Part 2: Tutorials

  The tutorials show you how to send messages, write classes, and start using the supplied class library. The chapter Object COBOL Tutorials briefly describes the subjects covered in the tutorials, and explains how you use them.

• Part 3: Object COBOL Programming

  Refer to the chapters in this section once you start programming.

  The first two chapters Using Objects in Programs and Class Programs deal with using and writing Object COBOL classes. If your interest is to be able to use Object COBOL classes supplied by others as building blocks, you only need to read the chapter Using Objects in Programs, but if you are going to write your own classes you need to read both.

  The chapter Extending a Class documents a Micro Focus feature for dynamically adding behavior to a class at run-time.

  The chapter Requirements-Based Vocabularies shows you how you can extend Object COBOL syntax and define your own verbs and functions for sending messages.

  The chapter Debugging Object COBOL Applications explains some of the extra facilities you will find useful in debugging any program which uses Object COBOL classes and objects.

  The chapter Compiling, Linking and Shipping OO Applications supplements the information supplied in the other manuals in your Object COBOL documentation set. It will help you get an application ready for delivery to end-users.

• Part 4: Class Library Frameworks

  Documents the main frameworks provided in the supplied Object COBOL Class Library. The Class Library is a big subject in its own right; the section Exploring the Class Library later in this chapter will help you to find your way around.

• Part 5: Appendices and Glossary

  Contains the appendix Descriptions of OO Run-time Switches. This is reference information on switches you can set to alter the behavior of OO applications at run-time.

  The glossary contains a list of the new terms introduced by this book.

1.2.2.1 Exploring the Class Library

The Class Library contains public classes and private classes. Private classes are not part of the public interface and are not fully documented - for an explanation of what Micro Focus means by public and private, see the sections Private Interface and Public Interface in the chapter Introduction to the Class Library.

To help you get started with the Class Library, we have provided four sources of information, moving from introductory and "how-to" information, to detailed reference information:

• Part 3 of this manual includes tutorials specifically about using different parts of the Class Library. These cover all the main areas of support provided by the Class Library for programmers. All the tutorials touch on some aspects of the Class Library. Work through the tutorials in the order supplied to get an overview of the Class Library.
  
  
• Part 4 of this manual has a general introduction to the Class Library, and information on the frameworks for each of the main types of class in the library. These explain how you use the main types of class in the Library, and the interfaces you should provide in your own objects, to enable them to work with the Class Library.
  
  
• The Class Library Reference contains a description of every public class. Private classes are listed, but not documented.

  For each class, it gives you a description of its use, and a list of all the public class and instance methods which the class either implements or inherits, except those inherited from Base. All classes inherit the methods in Base, so these are only documented under the description for Base.

• The source code to the Class Library is supplied with the product, Look at the source code if you need to supplement the information provided in the documentation. However, implementation details are considered private, which means that there is no guarantee they will not change between releases.

1.3 Learning More About Object-Orientation

The documentation supplied with Object COBOL will help you to start programming in Object COBOL. However, if you are new to OO, learning about the principles of Object-Oriented Design and Analysis (OOD and OOA) will enable you to make the best use of this new technology.

The reading list below suggests some texts you might want to start with. There are also several training organizations who run language-independent courses on OOD and OOA.

MERANT Training also runs Object COBOL programming courses.

1.3.1 Reading List

This is a short list of texts dealing with Object-Oriented methodologies and technologies.

Object COBOL Concepts