《PHP对象、模式与实践》之高级特性

高级特性
包括：
1.静态方法和属性（通过类而不是对象来访问数据和功能）
2.抽象类和接口（设计，实现分离）
3.错误处理（异常）
4.Final类和方法（限制继承）
5.拦截器（自动委托）
6.析构方法（对象销毁前的清理工作）
7.克隆对象（创建对象的副本）
8.把对象解析成字符串

PS，学会从内存的角度看代码。想象计算机的微观世界。

静态方法的小例子

<?php

class StaticExample{

    static public $aNum = 10;

    static public function sayHello(){

        print "hello";

    }

}

print StaticExample::$aNum."<br/>";

StaticExample::sayHello();

tips:
1.静态方法不能访问类中的普通属性，因为那些属性属于一个对象，但可以访问静态属性。
2.我们不能再对象中调用静态方法，因此不能再静态方法中使用伪变量$this。

静态方法的大例子

<?php

class ShopProduct{

    private $title;

    private $producerMainName;

    private $producerFirstName;

    protected $price;

    private $discount = 0;

    private $id = 0;

    function __construct($title,$firstName,$mainName,$price){

        $this->title = $title;

        $this->producerFirstName = $firstName;

        $this->producerMainName = $mainName;

        $this->price = $price;

    }

    public function setID($id){

        $this->id = $id;

    }

    public static function getInstance($id,PDO $pdo){

        $query = "select * from products where id= '$id'";

        $stmt = $pdo->query($query);

        $row = $stmt->fetch();

        if(empty($row)){

            return null;

        }

        if($row['type'] == "book"){

            $product = new BookProduct($row['title'],

                $row['firstname'],

                $row['mainname'],

                $row['price'],

                $row['numpages']

                );

        }else if($row['type'] == "cd"){

            $product = new CdProduct($row['title'],

                $row['firstname'],

                $row['mainname'],

                $row['price'],

                $row['playLength']

                );

        }else{

            $product = new ShopProduct($row['title'],

                $row['firstname'],

                $row['mainname'],

                $row['price']

                );

        }

        $product->setId($row['id']);

        $product->setDiscount($row['discount']);

        return $product;

    }

    public function getProducerFirstName(){

        return $this->producerFirstName;

    }

    public function getProducerMainName(){

        return $this->producerMainName;

    }

    public function setDiscount($num){

        $this->discount = $num;

    }

    public function getDiscount(){

        return $this->discount;

    }

    public function getTitle(){

        return $this->title;

    }

    public function getPrice(){

        return ($this->price - $this->discount);

    }

    function getProducer(){

        return $this->producerFirstName." ".$this->producerMainName;

    }

    function getSummaryLine(){

        $base = "$this->title({$this->producerMainName},";

        $base .= "{$this->producerFirstName})";

        return $base;

    }

}

class CdProduct extends ShopProduct{

    private $playLength;

    function __construct($title,$firstName,$mainName,$price,$playLength){

        parent::__construct($title,$firstName,$mainName,$price);//继承父类的构造函数

        $this->playLength = $playLength;

    }

    function getPlayLength(){

        return $this->playLength;

    }

    function getSummaryLine(){

        $base = parent::getSummaryLine();

        $base .= ":playing time {$this->playLength}";

        return $base;

    }

}

class BookProduct extends ShopProduct{

    private $numPages = 0;

    function __construct($title,$firstName,$mainName,$price,$numPages){

        parent::__construct($title,$firstName,$mainName,$price);

        $this->numPages = $numPages;

    }

    function getnumPages(){

        return $this->numPages;

    }

    function getSummaryLine(){

        $base = parent::getSummaryLine();

        $base .= ":page count {$this->numPages}";

        return $base;

    }

}

$dsn = "sqlite:C:/Users/Administrator/Desktop/shop.db";

$pdo = new PDO($dsn,null,null);

$pdo->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);

$obj = ShopProduct::getInstance(1,$pdo);

echo $obj->getSummaryLine();

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《PHP对象、模式与实践》之高级特性

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