Develop the General-Class for the Business Object 'Project' - Fat-Client-Development

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Last revision of this document:
2006-08-15

Business Objects are entities that keep together data belonging to one 'business-area'; e.g. an invoice with a 'header' and several 'positions'. Business Objects can contain data that is physically stored on different database-tables.

For the theory about Business Objects please consult Using Business Objects to handle data-storage and retrieval.

The General Class, which is developed in this step, contents all variables and methods of a Business Object that are needed on both the Client-Side and the Server-Side. It also contains Constants to signal a completion-status (either a completion as expected or unexpected errors) of the method.

`Preface:`

If you came to this document to get a guideline for developing a Business Object, I recommend to start with the document Business Object, Overview – Advanced Java Fat-Client-Development or go directly to the ToDo-List in document Business Object, General Class – Advanced Java Fat-Client-Development.

As classes for Business Objects have a critical mission within an application, preference was given to performance if there has to be made a decision between understandability and performance. I hope, that the comments placed in the code will help you to understand what intention is behind the code.

`Credits:`

Too numerous to mention; the idea is available in dozens of versions – I refined a lot of ideas into my system.

Prerequisites:

JS_FC01j – Develop the Base Class for Business Objects completed - and its prerequisites too.
To get the ideas and the theory of Business Objects it is recommended to browse the following documents:
Using Business Objects to handle data-storage and retrieval and
Business Object, Overview – Advanced Java Fat-Client-Development.

`Create the General Class for the Business Object 'Project':`

Let us start with a very small Business Object; it just contains 3 variables: * the Project-Code which identifies the Project the Error-Messages (designed later) are for; * the Language-Code which is the 2 character ISO-code for the language the Error-Messages are and * the directory where the file with the language-specific Error-Message in XML-structure is written out.

To create the class, right click onto the project 'JS_FC01' and select >New>Class
Enter the Package (js_errdb.bo), the (Class-)Name (JS_ErrDB_Project_BO), enter or 'Browse' the Superclass (js_base.bo.JSBS_BO) and check that no checkbox is selected; then click the [Finish] button.
Eclipse has already generated a template and the individual code can be entered. Please see the code to be entered at JS_ErrDB_Project_BO - or copy it from there ;-) .
A list with the major steps to do follows.

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`Code a method to copy the values from one object to another:`

Define the business variables of the Business Object. In this Business Object only 3 variables exist: /* * Project-Code; that is a shortcut for the Project. */ public String ProjectCode = ""; /* * Language-Code; that is the ISO-CODE for the language the Error-Messages are in. */ public String LanguageCode = ""; /* * Directory where the file with the language-specific error-messages is * written out when the file with the XML-structure is generated. */ public String TargetDirectory = "";

`Code a method to copy the values from one object to another:`

A method to copy all values from another Business Object (of the same class) is needed by every Business Object. /* * -------------------- * Method to copy the values from another object into this object. */ public void getJS_ErrDB_Project_BO(JS_ErrDB_Project_BO parmJS_ErrDB_Project_BO) { /* * Use the method of the super-class to copy the Common Attributes, * StatusCode and StatusMsg. */ super.getJSBS_BO(parmJS_ErrDB_Project_BO); ProjectCode = parmJS_ErrDB_Project_BO.ProjectCode; LanguageCode = parmJS_ErrDB_Project_BO.LanguageCode; TargetDirectory = parmJS_ErrDB_Project_BO.TargetDirectory; }

`Code a method to compare if the values of two Business Objects are different:`

To decide, if at least one Business Attribute was changed, a method to compare has to be implemented. Among others, this method is used to enable or disable buttons or to decide, if the database really has to be updated when the user sends a 'store' but has not changed any values. /* * -------------------- * Method to compare two Business Objects and check if * at least one of the Business Attributes is different. */ public boolean isDifferent(JS_ErrDB_Project_BO parmJS_ErrDB_Project_BO) { if (this.ProjectCode.compareTo(parmJS_ErrDB_Project_BO.ProjectCode) != 0) return true; if (this.LanguageCode.compareTo(parmJS_ErrDB_Project_BO.LanguageCode) != 0) return true; if (this.TargetDirectory.compareTo(parmJS_ErrDB_Project_BO.TargetDirectory) != 0) return true; return false; }

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`Next Steps:`

With the General Class finished, the derivation for the Client-Side can be developed. Aside from implementing the special methods for the client side, the next step deals with defining the Business Object as a variable in the class for the task frame and calling the relevant methods when the user clicks the button for 'store'.. JS_FC01l - Develop the Client-Side Class for the Business Object 'Project'.