Perl Tutorials - Herong's Tutorial Examples - Version 5.32, by Dr. Herong Yang
Class Variables and Object Variables
This section provides a tutorial example on how to define and use class variables and object variables. Class variables are stored at the class (package) level. Object variables are stored in the object. If an object is a reference of a hash variable, object variables are really hash keys and values.
Using Package Level Variables as Class Variables
In Perl, all package level variables are class variables. There is no private variable concept in Perl. All variables are publicly accessible in the same way as package variables.
Using Hash Entries to Store Object Variables
As you can see in the previous section, you can bless a reference of any "thing" into an object of a specific class.
The number and type of object variables you can use depend on the data type you select for the references:
In order to define object variables, we must create objects with references of the same data type for the same class. Using references of different data types for the same class will cause confusion to class and object methods.
Since objects are references, accessing object variables can be done in the same way as accessing references.
Here is a tutorial program to show you how to handle class variables and object variables:
#- ObjectVariableTest.pl #- Copyright (c) 1999 by Dr. Herong Yang, http://www.herongyang.com/ # package Account; $euroRate = 0.85; sub print { my $this = shift; my $currency = shift; my $balance = $$this{"Balance"}; $balance *= $euroRate if ($currency eq "EURO"); print("Printing account...\n"); print(" Name = ",$$this{"Name"},"\n"); print(" Type = ",$$this{"Type"},"\n"); print(" Balance = ",$balance,"\n"); } sub deposit { my $this = shift; my $amount = shift; $$this{"Balance"} += $amount; } sub setEuroRate { my $class = shift; $euroRate = shift; } package main; %myAccount = {}; $myAccount{"Name"} = "Herong Yang"; $myAccount{"Type"} = "Checking"; $myAccount{"Balance"} = 100.00; $myObj = \%myAccount; bless($myObj,Account); %hisAccount = {}; $hisAccount{"Name"} = "Mike Clinton"; $hisAccount{"Type"} = "Saving"; $hisAccount{"Balance"} = 999.00; $hisObj = \%hisAccount; bless($hisObj,Account); print("\nTest 1:\n"); $myObj->print(); $hisObj->print(); print("\nTest 2:\n"); $myObj->deposit(-25.00); $hisObj->deposit(99.00); $myObj->print(); $hisObj->print(); print("\nTest 3:\n"); $myObj->print("EURO"); $hisObj->print("EURO"); print("\nTest 4:\n"); Account->setEuroRate(0.80); $myObj->print("EURO"); $hisObj->print("EURO"); exit;
Obviously, $euroRate is used as a class variable. Keys "Name", "Type" and "Balance" in the hash are used as object variables. Here is the output of the tutorial program:
Test 1: Printing account... Name = Herong Yang Type = Checking Balance = 100 Printing account... Name = Mike Clinton Type = Saving Balance = 999 Test 2: Printing account... Name = Herong Yang Type = Checking Balance = 75 Printing account... Name = Mike Clinton Type = Saving Balance = 1098 Test 3: Printing account... Name = Herong Yang Type = Checking Balance = 63.75 Printing account... Name = Mike Clinton Type = Saving Balance = 933.3 Test 4: Printing account... Name = Herong Yang Type = Checking Balance = 60 Printing account... Name = Mike Clinton Type = Saving Balance = 878.4
Table of Contents
Data Types: Values and Variables
Expressions, Operations and Simple Statements
Name Spaces and Perl Module Files
Hard References - Addresses of Memory Objects
►Objects (or References) and Classes (or Packages)
Basic Concepts of Classes and Objects
Invoking Package Subroutines as Class Methods
bless() - Converting References to Objects
Invoking Package Subroutines as Object Methods
►Class Variables and Object Variables
new() Method - Creating Objects by the Class
CalendarClass.pm - A Perl Class Example
Typeglob and Importing Identifiers from Other Packages
String Built-in Functions and Performance
File Handles and Data Input/Output
Open Directories and Read File Names
File System Functions and Operations
Converting Perl Script to Executable Binary
Socket Communication Over the Internet
XML::Simple Module - XML Parser and Generator
SOAP::Lite - SOAP Server-Client Communication Module
Perl Programs as IIS Server CGI Scripts
CGI (Common Gateway Interface)
XML-RPC - Remote Procedure Call with XML and HTTP
RPC::XML - Perl Implementation of XML-RPC
Integrating Perl with Apache Web Server
CGI.pm Module for Building Web Pages