PHP物件導向深入研究之【繼承】，減少程式碼重複

桃子紅了吶發表於2017-01-29

繼承

先看兩個類

<?php
class CdProduct {
    public $playLength; // 播放時間
    public $title;
    public $producerMainName;
    public $producerFirstName;
    public $price;

    function __construct(   $title, $firstName,
                            $mainName, $price,
                            $playLength ) {
        $this->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; // 看的頁數
    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 "
";

$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine();
print "
";
?>
輸出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

　點評：這兩個類，程式碼重複性太高，有相同性，也有差異性。不如用繼承來簡化處理。

採用繼承來處理

<?php
class ShopProduct {
    public $numPages;
    public $playLength;
    public $title;
    public $producerMainName;
    public $producerFirstName;
    public $price;

    function __construct(   $title, $firstName,
                            $mainName, $price,
                            $numPages=0, $playLength=0 ) {
        $this->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() { // 增加屬於自己的方法
        return $this->playLength;
    }

    function getSummaryLine() { // 改造了父類的方法
        $base  = "{$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 "
";

$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine();
print "
";

?>
輸出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

點評：繼承處理很好的解決了差異性，相通性問題。

進一步優化處理

<?php
class ShopProduct {
    // 抽離出共有屬性
    public $title;
    public $producerMainName;
    public $producerFirstName;
    public $price;

    function __construct(   $title, $firstName,
                            $mainName, $price ) {
        $this->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 {
    // 抽離出屬於自己特有的屬性
    public $playLength;

    function __construct(   $title, $firstName,
                            $mainName, $price, $playLength ) {
        parent::__construct(    $title, $firstName,
                                $mainName, $price ); // 繼承父類的建構函式
        $this->playLength = $playLength; // 處理自己專有的屬性
    }

    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 "
";

$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine();
print "
";

?>
輸出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

點評：這裡把共有屬性在父類中，其他個性屬性放在自己的類中處理。並設定自己的構造方法，繼承父類的構造方法。

進一步繼承父類的方法

<?php
class ShopProduct {
    public $title;
    public $producerMainName;
    public $producerFirstName;
    public $price;

    function __construct(   $title, $firstName,
                            $mainName, $price ) {
        $this->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 "
";

$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine();
print "
";

?>
輸出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

點評：同樣的結果，可以優化優化再優化。這裡繼承父類的方法。parent::getSummaryLine()。不過這個用的比較少。

繼續新增一些有意思的內容

<?php
class ShopProduct {
    private $title;
    private $discount = 0;
    private $producerMainName;
    private $producerFirstName;
    protected $price;

    function __construct(   $title, $firstName,
                            $mainName, $price ) {
        $this->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 $product1->getSummaryLine();
print "
";
print "price: {$product1->getPrice()}
";

$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
$product2->setDiscount( 3 ); // 折扣對book無效
print $product2->getSummaryLine();
print "
";
print "price: {$product2->getPrice()}
";

?>
輸出：
cd1 ( bobbleson, bob ): playing time - 50
price: 1
book1 ( harrelson, harry ): page count - 30
price: 4

點評:父類新增了折扣，book繼承之後，修改了getPrice方法，所以折扣對book無效。

私有化屬性，通過方法來設定與獲取

<?php
class ShopProduct {
    // 私有化屬性，通過方法來設定與獲取
    private $title;
    private $producerMainName;
    private $producerFirstName;
    protected $price;
    private $discount = 0;

    public function __construct(   $title, $firstName,
                            $mainName, $price ) {
        $this->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()."
";
$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine()."
";
?>

輸出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

點評：這裡進一步私有化了屬性，要想獲取只能通過方法。這樣就確保了安全性。

本文轉自TBHacker部落格園部落格，原文連結：http://www.cnblogs.com/jiqing9006/p/5169350.html，如需轉載請自行聯絡原作者

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