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Patterns

Patterns are ways to describe best practices and good designs. They show a flexible solution to common programming problems.

Factory

The Factory pattern allows for the instantiation of objects at runtime. It is called a Factory Pattern since it is responsible for "manufacturing" an object. A Parameterized Factory receives the name of the class to instantiate as argument.

Example 19-25. Parameterized Factory Method


<?php
class Example
{
    // The parameterized factory method
    public static function factory($type)
    {
        if (include_once 'Drivers/' . $type . '.php') {
            $classname = 'Driver_' . $type;
            return new $classname;
        } else {
            throw new Exception ('Driver not found');
        }
    }
}
?>

Defining this method in a class allows drivers to be loaded on the fly. If the Example class was a database abstraction class, loading a MySQL and SQLite driver could be done as follows:


<?php
// Load a MySQL Driver
$mysql = Example::factory('MySQL');

// Load a SQLite Driver
$sqlite = Example::factory('SQLite');
?>

Singleton

The Singleton pattern applies to situations in which there needs to be a single instance of a class. The most common example of this is a database connection. Implementing this pattern allows a programmer to make this single instance easily accessible by many other objects.

Example 19-26. Singleton Function


<?php
class Example
{
    // Hold an instance of the class
    private static $instance;
    
    // A private constructor; prevents direct creation of object
    private function __construct() 
    {
        echo 'I am constructed';
    }

    // The singleton method
    public static function singleton() 
    {
        if (!isset(self::$instance)) {
            $c = __CLASS__;
            self::$instance = new $c;
        }

        return self::$instance;
    }
    
    // Example method
    public function bark()
    {
        echo 'Woof!';
    }

    // Prevent users to clone the instance
    public function __clone()
    {
        trigger_error('Clone is not allowed.', E_USER_ERROR);
    }

}

?>

This allows a single instance of the Example class to be retrieved.


<?php
// This would fail because the constructor is private
$test = new Example;

// This will always retrieve a single instance of the class
$test = Example::singleton();
$test->bark();

// This will issue an E_USER_ERROR.
$test_clone = clone $test;

?>

Alden Hosting offers private JVM (Java Virtual Machine), Java Server Pages (JSP), Servlets, and Servlets Manager with our Web Hosting Plans WEB 4 PLAN and WEB 5 PLAN , WEB 6 PLAN .

JAVA, JSP, SERVLETS, TOMCAT, SERVLETS MANAGER,
Private JVM (Java Virtual Machine),
Private Tomcat Server

Patterns

Factory

Singleton

JAVA, JSP, SERVLETS, TOMCAT, SERVLETS MANAGER,
Private JVM (Java Virtual Machine),
Private Tomcat Server

JAVA, JSP, SERVLETS, TOMCAT, SERVLETS MANAGER, Private JVM (Java Virtual Machine), Private Tomcat Server

Patterns

Factory

Singleton

JAVA, JSP, SERVLETS, TOMCAT, SERVLETS MANAGER, Private JVM (Java Virtual Machine), Private Tomcat Server

JAVA, JSP, SERVLETS, TOMCAT, SERVLETS MANAGER,
Private JVM (Java Virtual Machine),
Private Tomcat Server

JAVA, JSP, SERVLETS, TOMCAT, SERVLETS MANAGER,
Private JVM (Java Virtual Machine),
Private Tomcat Server