The @name and @description variables are assigned values in the initialize method when a new Thing object is created.
Instance variables generally cannot be directly accessed from the world outside the class itself.
To obtain the value of each variable, you need a get accessor method such as get_name.
In order to assign a new value, you need a set accessor method such as set_name.
class Thing def initialize( aName, aDescription ) @name = aName # from ww w . jav a 2 s . c o m @description = aDescription end def get_name return @name end def set_name( aName ) @name = aName end def get_description return @description end def set_description( aDescription ) @description = aDescription end end class Product < Thing def initialize( aName, aDescription, aValue ) super( aName, aDescription ) @value = aValue end def get_value return @value end def set_value( aValue ) @value = aValue end end
Product class is declared:
class Product < Thing
The left angle bracket < indicates that Product is a subclass, or descendant, of Thing.
It inherits the data (variables) and behavior (methods) from the Thing class.
Since the methods get_name, set_name, get_description, and set_description exist in the ancestor class (Thing), these methods don't need to be re-coded in the descendant class (Product).
The Product class has one additional piece of data, its value (@value).
We have written get and set accessors for this.
When a new Product object is created, its initialize method is automatically called.
A Product has three variables to initialize (@name, @description, and @value), so its initialize method takes three arguments.
The first two arguments are passed, using the super keyword, to the initialize method of the superclass (Thing) so that the Thing class's initialize method can deal with them:
super( aName, aDescription )
When used inside a method, the super keyword calls a method with the same name as the current method in the ancestor or superclass.
If the super keyword is used on its own, without any arguments being specified, all the arguments sent to the current method are passed to the ancestor method.
If a specific list of arguments is supplied, then only these are passed to the method of the ancestor class.