继承

先看两个类


     title             = $title;        $this->producerFirstName = $firstName;        $this->producerMainName  = $mainName;        $this->price             = $price;        $this->playLength        = $playLength;    }    function getPlayLength() {        return $this->playLength;    }    function getSummaryLine() {        $base  = "{$this->title} ( {$this->producerMainName}, ";        $base .= "{$this->producerFirstName} )";        $base .= ": playing time - {$this->playLength}";        return $base;    }    function getProducer() {        return "{$this->producerFirstName}".               " {$this->producerMainName}";    }}class BookProduct {    public $numPages; // 看的页数    public $title;    public $producerMainName;    public $producerFirstName;    public $price;    function __construct(   $title, $firstName,                            $mainName, $price,                            $numPages ) {        $this->title             = $title;        $this->producerFirstName = $firstName;        $this->producerMainName  = $mainName;        $this->price             = $price;        $this->numPages          = $numPages;    }    function getNumberOfPages() {        return $this->numPages;    }    function getSummaryLine() {        $base  = "{$this->title} ( {$this->producerMainName}, ";        $base .= "{$this->producerFirstName} )";        $base .= ": page count - {$this->numPages}";        return $base;    }    function getProducer() {        return "{$this->producerFirstName}".               " {$this->producerMainName}";    }}$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );print $product1->getSummaryLine();print "\n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine();print "\n";?>输出：cd1 ( bobbleson, bob ): playing time - 50book1 ( harrelson, harry ): page count - 30

　点评：这两个类，代码重复性太高，有相同性，也有差异性。不如用继承来简化处理。

采用继承来处理


     title             = $title;        $this->producerFirstName = $firstName;        $this->producerMainName  = $mainName;        $this->price             = $price;        $this->numPages          = $numPages;        $this->playLength        = $playLength;    }    function getProducer() {        return "{$this->producerFirstName}".               " {$this->producerMainName}";    }    function getSummaryLine() {        $base  = "$this->title ( {$this->producerMainName}, ";        $base .= "{$this->producerFirstName} )";        return $base;    }}class CdProduct extends ShopProduct {    function getPlayLength() { // 增加属于自己的方法        return $this->playLength;    }    function getSummaryLine() { // 改造了父类的方法        $base  = "{$this->title} ( {$this->producerMainName}, ";        $base .= "{$this->producerFirstName} )";        $base .= ": playing time - {$this->playLength}";        return $base;    }}class BookProduct extends ShopProduct {    function getNumberOfPages() {        return $this->numPages;    }    function getSummaryLine() {        $base  = "{$this->title} ( {$this->producerMainName}, ";        $base .= "{$this->producerFirstName} )";        $base .= ": page count - {$this->numPages}";        return $base;    }}$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, null, 50 );print $product1->getSummaryLine();print "\n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine();print "\n";?>输出：cd1 ( bobbleson, bob ): playing time - 50book1 ( harrelson, harry ): page count - 30

点评：继承处理很好的解决了差异性，相通性问题。

进一步优化处理


     title             = $title;        $this->producerFirstName = $firstName;        $this->producerMainName  = $mainName;        $this->price             = $price;    }    function getProducer() {        return "{$this->producerFirstName}".               " {$this->producerMainName}";    }    function getSummaryLine() {        $base  = "{$this->title} ( {$this->producerMainName}, ";        $base .= "{$this->producerFirstName} )";        return $base;    }}class CdProduct extends ShopProduct {    // 抽离出属于自己特有的属性    public $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; // 处理自己专有的属性    }    function getPlayLength() {        return $this->playLength;    }    function getSummaryLine() {        $base  = "{$this->title} ( {$this->producerMainName}, ";        $base .= "{$this->producerFirstName} )";        $base .= ": playing time - {$this->playLength}";        return $base;    }}class BookProduct extends ShopProduct {    public $numPages;    function __construct(   $title, $firstName,                            $mainName, $price, $numPages ) {        parent::__construct(    $title, $firstName,                                $mainName, $price );        $this->numPages = $numPages;    }    function getNumberOfPages() {        return $this->numPages;    }    function getSummaryLine() {        $base  = "$this->title ( $this->producerMainName, ";        $base .= "$this->producerFirstName )";        $base .= ": page count - $this->numPages";        return $base;    }}$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );print $product1->getSummaryLine();print "\n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine();print "\n";?>输出：cd1 ( bobbleson, bob ): playing time - 50book1 ( harrelson, harry ): page count - 30

点评：这里把共有属性在父类中，其他个性属性放在自己的类中处理。并设置自己的构造方法，继承父类的构造方法。

进一步继承父类的方法


     title             = $title;        $this->producerFirstName = $firstName;        $this->producerMainName  = $mainName;        $this->price             = $price;    }    function getProducer() {        return "{$this->producerFirstName}".               " {$this->producerMainName}";    }    function getSummaryLine() {        $base  = "{$this->title} ( {$this->producerMainName}, ";        $base .= "{$this->producerFirstName} )";        return $base;    }}class CdProduct extends ShopProduct {    public $playLength;    function __construct(   $title, $firstName,                            $mainName, $price, $playLength ) {        parent::__construct(    $title, $firstName,                                $mainName, $price );        $this->playLength = $playLength;    }    function getPlayLength() {        return $this->playLength;    }    function getSummaryLine() {        $base = parent::getSummaryLine();        $base .= ": playing time - {$this->playLength}";        return $base;    }}class BookProduct extends ShopProduct {    public $numPages;    function __construct(   $title, $firstName,                            $mainName, $price, $numPages ) {        parent::__construct(    $title, $firstName,                                $mainName, $price );        $this->numPages = $numPages;    }    function getNumberOfPages() {        return $this->numPages;    }    function getSummaryLine() {        $base = parent::getSummaryLine();        $base .= ": page count - {$this->numPages}";        return $base;    }}$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );print $product1->getSummaryLine();print "\n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine();print "\n";?>输出：cd1 ( bobbleson, bob ): playing time - 50book1 ( harrelson, harry ): page count - 30

点评：同样的结果，可以优化优化再优化。这里继承父类的方法。parent::getSummaryLine()。不过这个用的比较少。

继续添加一些有意思的内容


     title             = $title;        $this->producerFirstName = $firstName;        $this->producerMainName  = $mainName;        $this->price             = $price;    }    function setDiscount( $num ) {        $this->discount=$num;    }    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 {    public $playLength;    function __construct(   $title, $firstName,                            $mainName, $price, $playLength ) {        parent::__construct(    $title, $firstName,                                $mainName, $price );        $this->playLength = $playLength;    }    function getPlayLength() {        return $this->playLength;    }    function getSummaryLine() {        $base = parent::getSummaryLine();        $base .= ": playing time - {$this->playLength}";        return $base;    }}class BookProduct extends ShopProduct {    public $numPages;    function __construct(   $title, $firstName,                            $mainName, $price, $numPages ) {        parent::__construct(    $title, $firstName,                                $mainName, $price );        $this->numPages = $numPages;    }    function getPrice() {        return $this->price;    }    function getNumberOfPages() {        return $this->numPages;    }    function getSummaryLine() {        $base = parent::getSummaryLine();        $base .= ": page count - {$this->numPages}";        return $base;    }}$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );$product1->setDiscount( 3 );print $product1->getSummaryLine();print "\n";print "price: {
       $product1->getPrice()}\n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );$product2->setDiscount( 3 ); // 折扣对book无效print $product2->getSummaryLine();print "\n";print "price: {
       $product2->getPrice()}\n";?>输出：cd1 ( bobbleson, bob ): playing time - 50price: 1book1 ( harrelson, harry ): page count - 30price: 4

点评:父类添加了折扣，book继承之后，修改了getPrice方法，所以折扣对book无效。

私有化属性，通过方法来设置与获取


     title             = $title;        $this->producerFirstName = $firstName;        $this->producerMainName  = $mainName;        $this->price             = $price;    }    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 - $this->discount);    }    public function getProducer() {        return "{$this->producerFirstName}".               " {$this->producerMainName}";    }    public function getSummaryLine() {        $base  = "{$this->title} ( {$this->producerMainName}, ";        $base .= "{$this->producerFirstName} )";        return $base;    }}class CdProduct extends ShopProduct {    private $playLength = 0;    public function __construct(   $title, $firstName,                            $mainName, $price, $playLength ) {        parent::__construct(    $title, $firstName,                                $mainName, $price );        $this->playLength = $playLength;    }    public function getPlayLength() {        return $this->playLength;    }    public function getSummaryLine() {        $base = parent::getSummaryLine();        $base .= ": playing time - {$this->playLength}";        return $base;    }}class BookProduct extends ShopProduct {    private $numPages = 0;    public function __construct(   $title, $firstName,                            $mainName, $price, $numPages ) {        parent::__construct(    $title, $firstName,                                $mainName, $price );        $this->numPages = $numPages;    }    public function getNumberOfPages() {        return $this->numPages;    }    public function getSummaryLine() {        $base = parent::getSummaryLine();        $base .= ": page count - {$this->numPages}";        return $base;    }    public function getPrice() {        return $this->price;    }}$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );print $product1->getSummaryLine()."\n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine()."\n";?>输出：cd1 ( bobbleson, bob ): playing time - 50book1 ( harrelson, harry ): page count - 30

点评：这里进一步私有化了属性，要想获取只能通过方法。这样就确保了安全性。

本文转自TBHacker博客园博客，原文链接：http://www.cnblogs.com/jiqing9006/p/5169350.html，如需转载请自行联系原作者