objects and web scripting

scripting typically involves creating objects in order to execute certain tasks to achieve a desired outcome. and so … how do i create an object? it sounds silly, really. but, honest … its abstract … a tough concept around which to wrap one’s head. its the core of modern-day programming, though. so i had better start getting it.

object creation involves 2 steps.

(1). create an object definition ~ the code containing methods and properties of the object. methods ~ directions for making the object. properties ~ characteristics that typify the object.

create a constructor function ~ a named group of 1 or more programming statements that can create new objects. note – by convention, capitalize the first letter of a constructor function.

add properties ~ identified by object name “dot” property name. refer to the newly created, not yet instantiated objects as “this”

objectName.propertyName = value

add methods ~ (methods = functions called from within the method.) name the method, assign a function. use action words when naming methods.  identified using the syntax below. (argument = input to subroutine … used to assign a value to a property of the new object)

objectName.methodName(arguement)

(2) instantiation ~ create an  instance of the newly defined object. specify a unique name for the new object. assign the object to the recently created object definition using the “new” keyword.

steps in object instantion ~ variable assigned a value ~ variable value passed as a parameter (parameters act as local copies of the argument) to the new object ~ parameter used to assign variable value to an object property ~ object property used by the object’s show method ~ show calls the object’s display method, which writs to the browser.

classes and encapsulation

Encapsulation refers to the design concept that each object carries its own data and provides a set of services that are involved in calling the objects methods. objects provide services by sending and receiving messages from other objects. encapsulation means users can access an object’s services and functionality, without having ready access to the object’s underlying data itself. encapsulation facilitates software design and development using a ‘block method’ as well as object reuse, information hiding, and control over each object’s ability to view other objects.

classes facilitate the encapsulation process, by defining object program logic and data fields. essentially, classes definitions describe the structure of executing objects ~ that is, they act as templates for the creation of new instances (known in the jargon as ‘instantiation’ ) of the class object. methods that exist at the object level, as opposed to the instance level, can access the data of all object instances in the class. methods that exist at the level of an object’s instance can only access that particular data. the goal of object-oriented programing becomes achieving a balance between the degree of linkages among the various classes of any program and the degree of consistency within each individual class.