PHP編程中的__clone()方法使用詳解

2020-03-22 20:18:42

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可以在對(duì)象類中定義一個(gè)__clone()方法來(lái)調(diào)整對(duì)象的克隆行為。此方法的代碼將在克隆操作期間執(zhí)行。除了將所有現(xiàn)有對(duì)象成員復(fù)制到目標(biāo)對(duì)象之外，還會(huì)執(zhí)行__clone()方法指定的操作。下面修改Corporate_Drone類，增加以下方法：
function __clone() { $this- tiecolor = "blue";之后，創(chuàng)建一個(gè)新的Corporate_Drone對(duì)象，增加employeeid成員的值，克隆這個(gè)對(duì)象，然后輸出一些數(shù)據(jù)，從而顯示克隆對(duì)象的tiecolor確實(shí)是通過(guò)__clone()方法設(shè)置的。示例代碼：
// Create new corporatedrone object $drone1 = new corporatedrone(); // Set the $drone1 employeeid member $drone1- setEmployeeID("12345"); // Clone the $drone1 object $drone2 = clone $drone1; // Set the $drone2 employeeid member $drone2- setEmployeeID("67890"); // Output the $drone1 and $drone2 employeeid members echo "drone1 employeeID: ".$drone1- getEmployeeID()." br / echo "drone2 employeeID: ".$drone2- getEmployeeID()." br / echo "drone2 tiecolor: ".$drone2- getTiecolor()." br / 程序運(yùn)行結(jié)果
drone1 employeeID: 12345drone2 employeeID: 67890drone2 tiecolor:再來(lái)一個(gè)小例子：
html' target='_blank'>class Fruit { private $name = "水果"; private $color = "顏色"; public function setName($name){ $this- name = $name; public function setColor($color){ $this- color = $color; function showColor(){ return $this- color.'的'.$this- name." br / function __destruct(){ echo "被吃掉了（對(duì)象被回收） br / $apple = new Fruit();$apple- setName("大蘋(píng)果");$apple- setColor("紅色");echo $apple- showColor();$clone_apple = $apple;$clone_apple- setName("小蘋(píng)果");$clone_apple- setColor("青色");echo $clone_apple- showColor();
clone方法克隆出了一個(gè)新的類，所以此時(shí)內(nèi)存中有兩個(gè)對(duì)象。php的__clone()方法對(duì)一個(gè)對(duì)象實(shí)例進(jìn)行的淺復(fù)制,對(duì)象內(nèi)的基本數(shù)值類型進(jìn)行的是傳值復(fù)制，而對(duì)象內(nèi)的對(duì)象型成員變量,如果不重寫(xiě)__clone方法,顯式的clone這個(gè)對(duì)象成員變量的話,這個(gè)成員變量就是傳引用復(fù)制,而不是生成一個(gè)新的對(duì)象.如下面一個(gè)例子的第28行注釋所說(shuō) class Account { public $balance; public function __construct($balance) { $this- balance = $balance; class Person { private $id; private $name; private $age; public $account; public function __construct($name, $age, Account $account) { $this- name = $name; $this- age = $age; $this- account = $account; public function setId($id) { $this- id = $id; public function __clone() { #復(fù)制方法,可在里面定義再clone是進(jìn)行的操作 $this- id = 0; $this- account = clone $this- account; #不加這一句,account在clone是會(huì)只被復(fù)制引用,其中一個(gè)account的balance被修改另一個(gè)也同樣會(huì)被修改 $person = new Person("peter", 15, new Account(1000)); $person- setId(1); $person2 = clone $person; $person2- account- balance = 250; var_dump($person, $person2);
復(fù)制代碼代碼如下:
object(Person)#1 (4) { ["id":"Person":private]= int(1) ["name":"Person":private]= string(5) "peter" ["age":"Person":private]= int(15) ["account"]= object(Account)#2 (1) { ["balance"]= int(1000) } } object(Person)#3 (4) { ["id":"Person":private]= int(0) ["name":"Person":private]= string(5) "peter" ["age":"Person":private]= int(15) ["account"]= object(Account)#4 (1) { ["balance"]= int(250) } }
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