《PHP对象、模式与实践》之高级特性-白红宇

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


     ";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


     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();