PHP5試用(一)
Jun 21, 2016 am 09:14 AM
php5
雖然 PHP5 還沒有正式發(fā)布（開發(fā)版本已經(jīng)提供下載），但我們現(xiàn)在就可以開始體驗一下新的版本 將要帶給我們的驚喜。在以下的介紹中，我們將重點講述 PHP5 中的三大特色功能。這三大特點為：
* 新的對象模式 (New Object Mode)
* 異常處理 (Exceptions)
* 名稱空間 (Namespace)
在開始之前，要聲明兩點：
* 文章中的例子為了說明如何操作，有些部分使用了 PHP4 的表現(xiàn)手段，這僅僅是為了提高文章的可讀性。
* 文章中描述的部分與 PHP5 的最終發(fā)布版可能會有一些出入
在 PHP5 沒有最終正式發(fā)布前，你可以隨時從 http://snaps.php.net 下載到最新的編譯版本來親自體驗一下 PHP5 所帶給我們這些嶄新的功能。
新的對象模式
PHP5 中的對象已經(jīng)進行了較系統(tǒng)、較全面的調(diào)整，現(xiàn)在的樣子可能看起來會有些類似于 Java。本小節(jié)著重講述 PHP5 中新的對象模式，并舉了一些較簡易的例子來說明。就讓本節(jié)成為你的 PHP5 之旅的一個新起點吧。：）
* 構(gòu)造函數(shù)和析構(gòu)函數(shù)
* 對象的引用
* 對象的克隆
* 對象中的私有、公共及受保護模式
* 接口 (Interfaces)
* 抽象類
* __call
* __set 和 __get
* 靜態(tài)成員
構(gòu)造函數(shù)和析構(gòu)函數(shù)
在 PHP4 中，當(dāng)函數(shù)與對象同名時，這個函數(shù)將成為該對象的構(gòu)造函數(shù)，并且在 PHP4 中沒有析構(gòu)函數(shù)的概念。
在 PHP5 中，構(gòu)造函數(shù)被統(tǒng)一命名為 __construct，并且引入了析構(gòu)函數(shù)的概念，被統(tǒng)一命名為 __destruct。
例一：構(gòu)造函數(shù)和析構(gòu)函數(shù)
class foo {
var $x;
function __construct($x) {
$this->x = $x;
}
function display() {
print($this->x);
}
function __destruct() {
print("bye bye");
}
}
$o1 = new foo(4);
$o1->display();
?>
在上面的例子中，當(dāng)你終止調(diào)用 foo 類的時候，其析構(gòu)函數(shù)將會被調(diào)用，上例中會輸出 “bye bye”。
對象的引用
眾所周知，在PHP4 中，傳遞變量給一個函數(shù)或方法，實際是把這個變量做了一次復(fù)制，也就意味著你傳給函數(shù)或方法的是這個變量的一個副本，除非你使用了引用符號 “&” 來聲明是要做一個引用，而不是一個 Copy。在 PHP5 中，對象總是以引用的形式存在的，對象中的賦值操作同樣也都是一個引用操作。
例二：對象的引用
class foo {
var $x;
function setX($x) {
$this->x = $x;
}
function getX() {
return $this->x;
}
}
$o1 = new foo;
$o1->setX(4);
$o2 = $o1;
$o1->setX(5);
if($o1->getX() == $o2->getX()) print("Oh my god!");
?>
對象的克隆
如上所述，當(dāng)一個對象始終以引用的形式來被調(diào)用時，如果我想得到該對象的一個副本，該怎么辦呢？PHP5 提供了一個新的功能，就是對象的克隆，語法為 __clone。
例三：對象的克隆
class foo {
var $x;
function setX($x) {
$this->x = $x;
}
function getX() {
return $this->x;
}
}
$o1 = new foo;
$o1->setX(4);
$o2 = $o1->__clone();
$o1->setX(5); if($o1->getX() != $o2->getX()) print("Copies are independant");
?>
對象克隆的方法在其它很多應(yīng)用程序語言中都是存在的，所以你不必擔(dān)心它的穩(wěn)定性。：）
對象中的私有、公共及保護模式
PHP4 中，一個對象的所有方法和變量都是公共的，這意味著你可以在一個對象的外部操作其中的任意一個變量和方法。PHP5 引入了三種新的用來控制這種存取權(quán)限的模式，它們是：公共的(Public)、受保護的(Protected)及私有的(Private)。
公共模式(Public):允許在對象外部進行操作控制。
私有模式(Private):只允許本對象內(nèi)的方法對其進行操作控制。
受保護模式(Protected)：允許本對象及其父對象對其進行操作控制。
例四： 對象中的私有、公共及受保護模式
class foo {
private $x;
public function public_foo() {
print("I'm public");
}
protected function protected_foo() {
$this->private_foo(); //Ok because we are in the same class we can call private methods
print("I'm protected");
}
private function private_foo() {
$this->x = 3;
print("I'm private");
}
}
class foo2 extends foo {
public function display() {
$this->protected_foo();
$this->public_foo();
// $this->private_foo(); // Invalid! the function is private in the base class
}
} $x = new foo();
$x->public_foo();
//$x->protected_foo(); //Invalid cannot call protected methods outside the class and derived classes
//$x->private_foo(); //Invalid private methods can only be used inside the class $x2 = new foo2();
$x2->display();
?>
提示：對象中的變量總是以私有形式存在的，直接操作一個對象中的變量不是一個好的面向?qū)ο缶幊痰牧?xí)慣，更好的辦法是把你想要的變量交給一個對象的方法去處理。
接口 (Interfaces)
眾所周知，PHP4 中的對象支持繼承，要使一個對象成為另一個對象的派生類，你需要使用類似 “class foo extends parent” 的代碼來控制。 PHP4 和 PHP5 中，一個對象都僅能繼承一次，多重繼承是不被支持的。不過，在 PHP5 中產(chǎn)生了一個新的名詞：接口，接口是一個沒有具體處理代碼的特殊對象，它僅僅定義了一些方法的名稱及參數(shù)，此后的對象就可以方便的使用 'implement' 關(guān)鍵字把需要的接口整合起來，然后再加入具體的執(zhí)行代碼。
例五：接口
interface displayable {
function display();
}
interface printable {
function doprint();
}
class foo implements displayable,printable {
function display() {
// code
} function doprint() {
// code
}
}
?>
這對提高代碼的可讀性及通俗性有很大的幫助，通過上面的例子可以看到，對象 foo 包含了 displayable 和 printable 兩個接口，這時我們就可以清楚的知道，對象 foo 一定會有一個 display() 方法和一個 print() 方法，只需要去了解接口部分，你就可以輕易的操作該對象而不必去關(guān)心對象的內(nèi)部是如何運作的。
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