PHP面向对象深入研究之【对象生成】

对象

看个例子

<?php
abstract class Employee { // 雇员
    protected $name;
    function __construct( $name ) {
        $this->name = $name;
    }
    abstract function fire();
}

class Minion extends Employee { // 奴隶 继承 雇员
    function fire() {
        print "{$this->name}: I'll clear my desk\n";
    }
}

class NastyBoss { // 坏老板
    private $employees = array();

    function addEmployee( $employeeName ) { // 添加员工
        $this->employees[] = new Minion( $employeeName ); // 代码灵活性受到限制
    }

    function projectFails() {
        if ( count( $this->employees ) > 0 ) {
            $emp = array_pop( $this->employees );
            $emp->fire(); // 炒鱿鱼
        }
    }
}

$boss = new NastyBoss();
$boss->addEmployee( "harry" );
$boss->addEmployee( "bob" );
$boss->addEmployee( "mary" );
$boss->projectFails();

// output:
// mary: I'll clear my desk
?>

再看一个更具有灵活性的案例

<?php

abstract class Employee {
    protected $name;
    function __construct( $name ) {
        $this->name = $name;
    }
    abstract function fire();
}

class Minion extends Employee {
    function fire() {
        print "{$this->name}: I'll clear my desk\n";
    }
}

class NastyBoss {
    private $employees = array(); 

    function addEmployee( Employee $employee ) { // 传入对象
        $this->employees[] = $employee;
    }

    function projectFails() {
        if ( count( $this->employees ) ) {
            $emp = array_pop( $this->employees );
            $emp->fire();
        }
    }
}

// new Employee class...
class CluedUp extends Employee {
    function fire() {
        print "{$this->name}: I'll call my lawyer\n";
    }
}

$boss = new NastyBoss();
$boss->addEmployee( new Minion( "harry" ) ); // 直接以对象作为参数，更具有灵活性
$boss->addEmployee( new CluedUp( "bob" ) );
$boss->addEmployee( new Minion( "mary" ) );
$boss->projectFails();
$boss->projectFails();
$boss->projectFails();
// output:
// mary: I'll clear my desk
// bob: I'll call my lawyer
// harry: I'll clear my desk
?>

单例

<?php

class Preferences {
    private $props = array();
    private static $instance; // 私有的，静态属性

    private function __construct() { } // 无法实例化，私有的构造函数

    public static function getInstance() { // 返回对象 静态方法才可以被类访问，静态方法中要有静态属性
        if ( empty( self::$instance ) ) {
            self::$instance = new Preferences();
        }
        return self::$instance;
    }

    public function setProperty( $key, $val ) {
        $this->props[$key] = $val;
    }

    public function getProperty( $key ) {
        return $this->props[$key];
    }
}

$pref = Preferences::getInstance();
$pref->setProperty( "name", "matt" );

unset( $pref ); // remove the reference

$pref2 = Preferences::getInstance();
print $pref2->getProperty( "name" ) ."\n"; // demonstrate value is not lost
?>

点评：不能随意创建对象，只能通过Preferences::getInstance()来创建对象。

工厂模式

<?php

abstract class ApptEncoder {
    abstract function encode();
}

class BloggsApptEncoder extends ApptEncoder {
    function encode() {
        return "Appointment data encoded in BloggsCal format\n";
    }
}

class MegaApptEncoder extends ApptEncoder {
    function encode() {
        return "Appointment data encoded in MegaCal format\n";
    }
}

class CommsManager { // 负责生产Bloggs对象
    function getApptEncoder() {
        return new BloggsApptEncoder();
    }
}

$obj = new CommsManager();
$bloggs = $obj->getApptEncoder(); // 获取对象
print $bloggs->encode();
?>
output:
Appointment data encoded in BloggsCal format

进一步增加灵活性设置

<?php

abstract class ApptEncoder {
    abstract function encode();
}

class BloggsApptEncoder extends ApptEncoder {
    function encode() {
        return "Appointment data encoded in BloggsCal format\n";
    }
}

class MegaApptEncoder extends ApptEncoder {
    function encode() {
        return "Appointment data encoded in MegaCal format\n";
    }
}

class CommsManager {
    const BLOGGS = 1;
    const MEGA = 2;
    private $mode ;

    function __construct( $mode ) {
        $this->mode = $mode;
    }

    function getHeaderText() {
        switch ( $this->mode ) {
            case ( self::MEGA ):
                return "MegaCal header\n";
            default:
                return "BloggsCal header\n";
        }
    }
    function getApptEncoder() {
        switch ( $this->mode ) {
            case ( self::MEGA ):
                return new MegaApptEncoder();
            default:
                return new BloggsApptEncoder();
        }
    }
}

$man = new CommsManager( CommsManager::MEGA );
print ( get_class( $man->getApptEncoder() ) )."\n";
$man = new CommsManager( CommsManager::BLOGGS );
print ( get_class( $man->getApptEncoder() ) )."\n";
?>
output:
MegaApptEncoder
BloggsApptEncoder

工厂方法模式要把创建者类与要生产的产品类分离开来。

抽象工厂

通过抽象来来约束，成为一定的规矩。

<?php
abstract class ApptEncoder {
    abstract function encode();
}

class BloggsApptEncoder extends ApptEncoder {
    function encode() {
        return "Appointment data encoded in BloggsCal format\n";
    }
}

class MegaApptEncoder extends ApptEncoder {
    function encode() {
        return "Appointment data encoded in MegaCal format\n";
    }
}

abstract class CommsManager { // 预约
    abstract function getHeaderText();
    abstract function getApptEncoder();
    abstract function getTtdEncoder();
    abstract function getContactEncoder();
    abstract function getFooterText();
}

class BloggsCommsManager extends CommsManager {
    function getHeaderText() {
        return "BloggsCal header\n";
    }

    function getApptEncoder() {
        return new BloggsApptEncoder();
    }

    function getTtdEncoder() {
        return new BloggsTtdEncoder();
    }

    function getContactEncoder() {
        return new BloggsContactEncoder();
    }

    function getFooterText() {
        return "BloggsCal footer\n";
    }
}

class MegaCommsManager extends CommsManager {
    function getHeaderText() {
        return "MegaCal header\n";
    }

    function getApptEncoder() {
        return new MegaApptEncoder();
    }

    function getTtdEncoder() {
        return new MegaTtdEncoder();
    }

    function getContactEncoder() {
        return new MegaContactEncoder();
    }

    function getFooterText() {
        return "MegaCal footer\n";
    }
}

$mgr = new MegaCommsManager();
print $mgr->getHeaderText();
print $mgr->getApptEncoder()->encode(); // 对象调用方法，返回对象，继续调用方法。
print $mgr->getFooterText();

?>
output:
MegaCal header
Appointment data encoded in MegaCal format
MegaCal footer

更加牛逼的实现

<?php
// 根据类图，规划类的代码。从大局入手。
abstract class ApptEncoder {
    abstract function encode();
}

class BloggsApptEncoder extends ApptEncoder {
    function encode() {
        return "Appointment data encoded in BloggsCal format\n";
    }
}

class MegaApptEncoder extends ApptEncoder {
    function encode() {
        return "Appointment data encoded in MegaCal format\n";
    }
}

abstract class CommsManager {
    const APPT    = 1;
    const TTD     = 2;
    const CONTACT = 3;
    abstract function getHeaderText();
    abstract function make( $flag_int ); // int标记
    abstract function getFooterText();
}

class BloggsCommsManager extends CommsManager {
    function getHeaderText() {
        return "BloggsCal header\n";
    }
    function make( $flag_int ) {
        switch ( $flag_int ) {
            case self::APPT: // self直接控制常量
                return new BloggsApptEncoder();
            case self::CONTACT:
                return new BloggsContactEncoder();
            case self::TTD:
                return new BloggsTtdEncoder();
        }
    }

    function getFooterText() {
        return "BloggsCal footer\n";
    }
}

$mgr = new BloggsCommsManager();
print $mgr->getHeaderText();
print $mgr->make( CommsManager::APPT )->encode();
print $mgr->getFooterText();

?>
output:
BloggsCal header
Appointment data encoded in BloggsCal format
BloggsCal footer

原型模式

改造成一个保存具体产品的工厂类。

<?php

class Sea {} // 大海
class EarthSea extends Sea {}
class MarsSea extends Sea {}

class Plains {} // 平原
class EarthPlains extends Plains {}
class MarsPlains extends Plains {}

class Forest {} // 森林
class EarthForest extends Forest {}
class MarsForest extends Forest {}

class TerrainFactory { // 地域工厂
    private $sea;
    private $forest;
    private $plains;

    function __construct( Sea $sea, Plains $plains, Forest $forest ) { // 定义变量为类对象
        $this->sea = $sea;
        $this->plains = $plains;
        $this->forest = $forest;
    }

    function getSea( ) {
        return clone $this->sea; // 克隆
    }

    function getPlains( ) {
        return clone $this->plains;
    }

    function getForest( ) {
        return clone $this->forest;
    }
}

$factory = new TerrainFactory( new EarthSea(),
    new EarthPlains(),
    new EarthForest() );
print_r( $factory->getSea() );
print_r( $factory->getPlains() );
print_r( $factory->getForest() );
?>
output:
EarthSea Object
(
)
EarthPlains Object
(
)
EarthForest Object
(
)