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Home php教程 PHP源碼 對(duì)象模型

對(duì)象模型

Jun 08, 2016 pm 05:33 PM
php php5 private

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PHP5有一個(gè)單重繼續(xù)的,限制訪問(wèn)的,可以重載的對(duì)象模型. 本章稍后會(huì)具體討論的”繼續(xù)”,包含類間的父-子關(guān)系. 另外,PHP支持對(duì)屬性和方法的限制性訪問(wèn). 你可以聲明成員為private,不答應(yīng)外部類訪問(wèn). 最后,PHP答應(yīng)一個(gè)子類從它的父類中重載成員.

  file://haohappy注:PHP4中沒(méi)有private,只有public.private對(duì)于更好地實(shí)現(xiàn)封裝很有好處.

  PHP5的對(duì)象模型把對(duì)象看成與任何其它數(shù)據(jù)類型不同,通過(guò)引用來(lái)傳遞. PHP不要求你通過(guò)引用(reference)顯性傳遞和返回對(duì)象. 在本章的最后將會(huì)具體闡述基于句柄的對(duì)象模型. 它是PHP5中最重要的新特性.

  有了更直接的對(duì)象模型,基于句柄的體系有附加的優(yōu)勢(shì): 效率提高, 占用內(nèi)存少,并且具有更大的靈活性.

  在PHP的前幾個(gè)版本中,腳本默認(rèn)復(fù)制對(duì)象.現(xiàn)在PHP5只移動(dòng)句柄,需要更少的時(shí)間. 腳本執(zhí)行效率的提升是由于避免了不必要的復(fù)制. 在對(duì)象體系帶來(lái)復(fù)雜性的同時(shí),也帶來(lái)了執(zhí)行效率上的收益. 同時(shí),減少?gòu)?fù)制意味著占用更少的內(nèi)存,可以留出更多內(nèi)存給其它操作,這也使效率提高.

  file://haohappy注:基于句柄,就是說(shuō)兩個(gè)對(duì)象可以指向同一塊內(nèi)存,既減少了復(fù)制動(dòng)作,又減少對(duì)內(nèi)存的占用.

  Zand引擎2具有更大的靈活性. 一個(gè)令人興奮的發(fā)展是答應(yīng)析構(gòu)--在對(duì)象銷毀之前執(zhí)行一個(gè)類方法. 這對(duì)于利用內(nèi)存也很有好處,讓PHP清楚地知道什么時(shí)候沒(méi)有對(duì)象的引用,把空出的內(nèi)存分配到其它用途。

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