本文實例講述了PHP面向對象繼承用法。分享給大家供大家參考，具體如下：
繼承
先看兩個類
<?phpclass 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 $product1->getSummaryLine();print "/n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine();print "/n";?>輸出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30
點評：這兩個類，代碼重復性太高，有相同性，也有差異性。不如用繼承來簡化處理。
采用繼承來處理
<?phpclass 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() { // 增加屬于自己的方法 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 $product1->getSummaryLine();print "/n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine();print "/n";?>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
<?phpclass 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 { // 抽離出屬于自己特有的屬性 public $playLength; function __construct( $title, $firstName, $mainName, $price, $playLength ) { parent::__construct( $title, $firstName, $mainName, $price ); // 繼承父類的構造函數 $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 $product1->getSummaryLine();print "/n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine();print "/n";?>輸出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30
點評：這里把共有屬性在父類中，其他個性屬性放在自己的類中處理。并設置自己的構造方法，繼承父類的構造方法。
進一步繼承父類的方法
<?phpclass 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 $product1->getSummaryLine();print "/n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine();print "/n";?>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。這里繼承父類的方法。parent::getSummaryLine()。不過這個用的比較少。
繼續添加一些有意思的內容
<?phpclass 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 $product1->getSummaryLine();print "/n";print "price: {$product1->getPrice()}/n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );$product2->setDiscount( 3 ); // 折扣對book無效print $product2->getSummaryLine();print "/n";print "price: {$product2->getPrice()}/n";?>輸出：
cd1 ( bobbleson, bob ): playing time - 50
price: 1
book1 ( harrelson, harry ): page count - 30
price: 4
點評:父類添加了折扣，book繼承之后，修改了getPrice方法，所以折扣對book無效。
私有化屬性，通過方法來設置與獲取
<?phpclass ShopProduct { // 私有化屬性，通過方法來設置與獲取 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 $product1->getSummaryLine()."/n";$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );print $product2->getSummaryLine()."/n";?>輸出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30
點評：這里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。
希望本文所述對大家PHP程序設計有所幫助。
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