Difference between revisions of "CLASS"

Latest revision as of 11:33, 13 January 2010

Purpose

Create a user-defined class

Syntax

CLASS <class name> [OF | AS | EXTENDS <base class> [, ...]]

ENDCLASS

See Also

ACLASS(), ADDPROPERTY(), AMEMBERS(), CLASS - Methods, CLASS - Parameters, CLASS - Properties, CLASS - Scoping, COMPOBJ(), CREATEOBJECT(), DEFINE CLASS, DISPLAY CLASSES, DODEFAULT(), FOREACH, LIST CLASSES, LOADOBJECT(), METHOD, NEWOBJECT(), OBJECT(), PRINT_HTML(), PRINT_JSON(), PRINT_R(), PRINT_XML(), REMOVEPROPERTY(), REQUIRE_ONCE(), SAVEOBJECT(), SQL SELECT, WITH

Description

Fundamental to object-oriented programming is the concept of Objects and classes. An object is a self-contained unit of data and functions that manipulate that data. A class is a specification of an object. A class contains memory variable specifications known as properties and functions that perform actions on the object known as methods. An object is an instance of a class.

The NEW operator is used to define a new object based on a class. The class name must be postfixed with parentheses when the new operator is used. The syntax is therefore as follows:

<object> = NEW <class>()

e.g. myobject = new myclass()

The CLASS...ENDCLASS construct is used to create a user-defined class. The beginning of a class is specified with CLASS <class name>, where <class name> can be any valid name up to 32 characters. The ENDCLASS command is used to complete the class construct. The CLASS...ENDCLASS construct is built using the commands describe in this section. Any Recital command can be used in building methods in the class, however these commands cannot be used outside the method definition inside a CLASS...ENDCLASS construct.

OF | AS | EXTENDS <base-name> [, ...]

A key feature of the object-oriented code is reusability through a mechanism called inheritance, that is, one class can inherit the members and their implementation from another class. Building new classes out of existing classes allows for the reusing of proven classes and the incorporation of system classes into user defined classes. Inheritance enables developers to build a hierarchy of descending objects. The inheriting class is called a derived class, and the class from which the derived class inherits is called a base class. The OF | AS | EXTENDS clause is used to inherit the <base name>. You can inherit multiple classes by specifying a class name comma-separated list.

Example

class product
    public name
    public price
    procedure init(cName, nPrice)    // constructor
        name = cName
        price = nPrice
    endproc
    procedure display()
        echo "Product name is " + name + ", price is " + price + "\n"
    endproc
endclass
 
class car of product
    private color
endclass
 
class motorbike as product
    private size
endclass
 
class vehicle extends car, motorbike
    public manufacturer = "Ford"
    public yearDesigned
    procedure init(cName, nPrice)    // constructor
        manufacturer = cName
        name = cName
        price = nPrice
    endproc
    procedure display()
        dodefault()
        echo "Manufacturer is " + manufacturer + ", price is " + price + "\n"
    endproc
endclass
 
// create new objects
myobject = new vehicle("Ford", 20000)
myobject.display()
 
myobject = new motorbike("Honda", 1500)
myobject.display()

Products

Recital Server, Recital