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Home php教程 PHP源碼 面向?qū)ο缶幊?/span>

面向?qū)ο缶幊?/h1> Jun 08, 2016 pm 05:33 PM
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面向?qū)ο缶幊瘫辉O(shè)計來為大型軟件項目提供解決方案,尤其是多人合作的項目. 當(dāng)源代碼增長到一萬行甚至更多的時候,每一個更動都可能導(dǎo)致不希望的副作用. 這種情況發(fā)生于模塊間結(jié)成秘密聯(lián)盟的時候,就像第一次世界大戰(zhàn)前的歐洲.

//haohappy注:喻指模塊間的關(guān)聯(lián)度過高,相互依靠性太強(qiáng).更動一個模塊導(dǎo)致其它模塊也必須跟著更動.

  想像一下,假如有一個用來處理登錄的模塊答應(yīng)一個信用卡處理模塊來分享它的數(shù)據(jù)庫連接. 當(dāng)然出發(fā)點是好的,節(jié)省了進(jìn)行另一個數(shù)據(jù)庫連接的支出.然而有時,登錄處理模塊改變了其中一個變量的名字,就可能割斷了兩者間的協(xié)議.導(dǎo)致信用卡模塊的處理出錯,進(jìn)而導(dǎo)致處理的模塊出錯. 很快地,體系中所有無關(guān)的模塊都可能由此出錯.

  因此,我覺得有點戲劇性地,絕大多數(shù)程序員都對耦合和封裝心存感激. 耦合是兩個模塊間依靠程度的量度. 耦合越少越好.我們希望能夠從已有的項目中抽走一個模塊并在另一個新項目中使用.

我們也希望在某個模塊內(nèi)部大規(guī)模的更動而不用擔(dān)心對其他模塊的影響. 封裝的原則可以提供這個解決方案.模塊被看待成相對獨立,并且模塊間的數(shù)據(jù)通信通過接口來進(jìn)行. 模塊不通過彼此的變量名來窺探另一個模塊,它們通過函數(shù)來禮貌地發(fā)送請求.

  封裝是你可以在任何編程語言中使用的一個原則. 在PHP和許多面向過程的語言中,可以偷懶是很有誘惑的.沒有什么可以阻止你通過模塊來構(gòu)建一個假想的WEB. 面向?qū)ο缶幊淌鞘钩绦騿T不會違反封裝原則的一種方法.


  在面向?qū)ο缶幊讨?模塊被組織成一個個對象. 這些對象擁有方法和屬性. 從抽象的角度來看,方法是一個對象的所做的動作,而屬性是對象的特性.從編程角度來看,方法就是函數(shù)而屬性是變量. 在一個理想化的面向?qū)ο篌w系中,每個部份都是一個對象. 體系由對象及對象間通過方法來形成的聯(lián)系構(gòu)成.

  一個類定義了對象的屬性. 假如你在烘烤一組甜餅對象,那么類將會是甜餅機(jī). 類的屬性和方法是被調(diào)用的成員. 人們可以通過說出數(shù)據(jù)成員或者方法成員來表達(dá).


  每種語言提供了不同的途徑來訪問對象. PHP從C 中借用概念,提供一個數(shù)據(jù)類型用來在一個標(biāo)識符下包含函數(shù)和變量。最初設(shè)計PHP的時候,甚至PHP3被開發(fā)出時,PHP并不打算提供開發(fā)超過10萬行代碼的大型項目的能力。隨著PHP和Zend引擎的發(fā)展,開發(fā)大型項目變得有可能,但無論你的項目規(guī)模多大,用類來書寫你的腳本將可以讓代碼實現(xiàn)重用。這是一個好主意,非凡當(dāng)你愿意與別人分享你的代碼的時候。

  有關(guān)對象的想法是計算機(jī)科學(xué)上最令人興奮的概念之一。開始很難把握它,但我可以保證,一旦你把握了它,用它的思維來思考將會非常自然。

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