Release 10.1A: OpenEdge Getting Started:
Object-oriented Programming

Preface

This Preface contains the following sections:

Purpose
Audience
Organization
Typographical conventions
Examples of syntax descriptions
OpenEdge messages

Purpose

The Progress® 4GL has long supported the ability to create and program with objects built from persistent procedures (procedure-based objects). These objects feature and depend almost entirely on run-time management to organize them for use in an application. With OpenEdge® Release 10.1, the 4GL includes support for classes. Classes allow a Progress developer to create and program with objects built from user-defined classes (class-based objects) that can be defined and organized for use by an application at compile time. The developer can define and manage class-based objects using the standard features of object-oriented programming available in programming languages, such as Java. The developer can also use procedure-based and class-based objects together in a single application.

This manual introduces object-oriented programming using classes in the Progress 4GL and also describes how to work with class-based and procedure-based objects together.

Audience

A Progress developer who is thoroughly familiar with programming in the Progress 4GL. For more information, see OpenEdge Development: Progress 4GL Handbook .

It is also helpful, but not required, for the reader to be familiar with object-oriented programming concepts and have familiarity with another object-oriented programming language, such as Java.

Organization

Chapter 1 "Object-oriented Programming and the Progress 4GL"

Introduces support for classes in the Progress 4GL, compares and contrasts programming with procedures and programming with classes, and provides an overview of object-oriented programming for the Progress programmer.

Chapter 2 "Getting Started with Classes, Interfaces, and Objects"

Describes the syntax and provides examples of defining classes and interfaces, and describes basic object life-cycle management.

Chapter 3 "Designing Objects — Inheritance, Polymorphism, and Delegation"

Describes how to use inheritance, polymorphism, and delegation to design and organize class-based objects.

Chapter 4 "Programming with Class-based Objects"

Describes how to instantiate and program with class-based objects.

Chapter 5 "Programming with Class-based and Procedure-based Objects"

Describes how to use class-based and procedure-based objects in a Progress application.

Chapter 6 "Developing and Deploying Classes"

Describes how to use Progress 4GL development tools and 4GL features to create, compile, and deploy class files.

Typographical conventions

This manual uses the following typographical conventions:

Convention	Description
Bold	Bold typeface indicates commands or characters the user types, provides emphasis, or the names of user interface elements.
Italic	Italic typeface indicates the title of a document, or signifies new terms.
SMALL, BOLD CAPITAL LETTERS	Small, bold capital letters indicate OpenEdge® key functions and generic keyboard keys; for example, GET and CTRL.
KEY1+KEY2	A plus sign between key names indicates a simultaneous key sequence: you press and hold down the first key while pressing the second key. For example, CTRL+X.
KEY1 KEY2	A space between key names indicates a sequential key sequence: you press and release the first key, then press another key. For example, ESCAPE H.
Syntax:
Fixed width	A fixed-width font is used in syntax statements, code examples, system output, and filenames.
Fixed-width italics	Fixed-width italics indicate variables in syntax statements.
Fixed-width bold	Fixed-width bold indicates variables with special emphasis.
UPPERCASE fixed width	Uppercase words are Progress® 4GL language keywords. Although these are always shown in uppercase, you can type them in either uppercase or lowercase in a procedure.
	This icon (three arrows) introduces a multi-step procedure.
	This icon (one arrow) introduces a single-step procedure.
Period (.) or colon (:)	All statements except DO, FOR, FUNCTION, PROCEDURE, and REPEAT end with a period. DO, FOR, FUNCTION, PROCEDURE, and REPEAT statements can end with either a period or a colon.
[ ]	Large brackets indicate the items within them are optional.
[ ]	Small brackets are part of the Progress 4GL language.
{ }	Large braces indicate the items within them are required. They are used to simplify complex syntax diagrams.
{ }	Small braces are part of the Progress 4GL language. For example, a called external procedure must use braces when referencing arguments passed by a calling procedure.
|	A vertical bar indicates a choice.
...	Ellipses indicate repetition: you can choose one or more of the preceding items.

Examples of syntax descriptions

In this example, ACCUM is a keyword, and aggregate and expression are variables:

Syntax

ACCUM aggregate expression

FOR is one of the statements that can end with either a period or a colon, as in this example:

FOR EACH Customer:   DISPLAY Name. END.

In this example, STREAM stream, UNLESS-HIDDEN, and NO-ERROR are optional:

Syntax

DISPLAY [ STREAM stream ] [ UNLESS-HIDDEN ] [ NO-ERROR ]

In this example, the outer (small) brackets are part of the language, and the inner (large) brackets denote an optional item:

Syntax

INITIAL [ constant [ , constant ] ]

A called external procedure must use braces when referencing compile-time arguments passed by a calling procedure, as shown in this example:

Syntax

{ &argument-name }

In this example, EACH, FIRST, and LAST are optional, but you can choose only one of them:

Syntax

PRESELECT [ EACH | FIRST | LAST ] record-phrase

In this example, you must include two expressions, and optionally you can include more. Multiple expressions are separated by commas:

Syntax

MAXIMUM ( expression , expression [ , expression ] ... )

In this example, you must specify MESSAGE and at least one expression or SKIP [ (n) ], and any number of additional expression or SKIP [ ( n ) ] is allowed:

Syntax

MESSAGE { expression | SKIP [ ( n ) ] } ...

In this example, you must specify {include-file, then optionally any number of argument or &argument-name = "argument-value", and then terminate with }:

Syntax

{ include-file     [ argument | &argument-name = "argument-value" ] ... }

Long syntax descriptions split across lines

Some syntax descriptions are too long to fit on one line. When syntax descriptions are split across multiple lines, groups of optional and groups of required items are kept together in the required order.

In this example, WITH is followed by six optional items:

Syntax

WITH [ ACCUM max-length ] [ expression DOWN ]   [ CENTERED ] [ n COLUMNS ] [ SIDE-LABELS ]   [ STREAM-IO ]

Complex syntax descriptions with both required and optional elements

Some syntax descriptions are too complex to distinguish required and optional elements by bracketing only the optional elements. For such syntax, the descriptions include both braces (for required elements) and brackets (for optional elements).

In this example, ASSIGN requires either one or more field entries or one record. Options available with field or record are grouped with braces and brackets:

Syntax

ASSIGN   { [ FRAME frame ] { field [ = expression ] }             [ WHEN expression ] } ...        | { record [ EXCEPT field ... ] }

OpenEdge messages

OpenEdge displays several types of messages to inform you of routine and unusual occurrences:

Execution messages inform you of errors encountered while OpenEdge is running a procedure; for example, if OpenEdge cannot find a record with a specified index field value.
Compile messages inform you of errors found while OpenEdge is reading and analyzing a procedure before running it; for example, if a procedure references a table name that is not defined in the database.
Startup messages inform you of unusual conditions detected while OpenEdge is getting ready to execute; for example, if you entered an invalid startup parameter.

After displaying a message, OpenEdge proceeds in one of several ways:

Continues execution, subject to the error-processing actions that you specify or that are assumed as part of the procedure. This is the most common action taken after execution messages.
Returns to the Progress Procedure Editor, so you can correct an error in a procedure. This is the usual action taken after compiler messages.
Halts processing of a procedure and returns immediately to the Progress Procedure Editor. This does not happen often.
Terminates the current session.

OpenEdge messages end with a message number in parentheses. In this example, the message number is 200:

** Unknown table name table. (200)

If you encounter an error that terminates OpenEdge, note the message number before restarting.

Obtaining more information about OpenEdge messages

In Windows platforms, use OpenEdge online help to obtain more information about OpenEdge messages. Many OpenEdge tools include the following Help menu options to provide information about messages:

Choose Help Recent Messages to display detailed descriptions of the most recent OpenEdge message and all other messages returned in the current session.
Choose Help Messages and then type the message number to display a description of a specific OpenEdge message.
In the Progress Procedure Editor, press the HELP key or F1.

On UNIX platforms, use the Progress pro command to start a single-user mode character OpenEdge client session and view a brief description of a message by providing its number.

To use the pro command to obtain a message description by message number:

Start the Progress Procedure Editor:

install-dir/dlc/bin/pro

Press F3 to access the menu bar, then choose Help Messages.
Type the message number and press ENTER. Details about that message number appear.
Press F4 to close the message, press F3 to access the Progress Procedure Editor menu, and choose File Exit.