PHP编程中的__clone()方法使用详解

可以在对象类中定义一个__clone()方法来调整对象的克隆行为。此方法的代码将在克隆操作期间执行。除了将所有现有对象成员复制到目标对象之外，还会执行__clone()方法指定的操作。下面修改Corporate_Drone类，增加以下方法：

function __clone() { $this->tiecolor = "blue"; }

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之后，创建一个新的Corporate_Drone对象，增加employeeid成员的值，克隆这个对象，然后输出一些数据，从而显示克隆对象的tiecolor确实是通过__clone()方法设置的。示例代码：

<?php // 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()."
"; echo "drone2 employeeID: ".$drone2->getEmployeeID()."
"; echo "drone2 tiecolor: ".$drone2->getTiecolor()."
"; ?>

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程序运行结果

drone1 employeeID: 12345 drone2 employeeID: 67890 drone2 tiecolor:

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再来一个小例子：

<?php class Fruit { private $name = "水果"; private $color = "颜色"; public function setName($name){ $this->name = $name; } public function setColor($color){ $this->color = $color; } function showColor(){ return $this->color.'的'.$this->name."
"; } function __destruct(){ echo "被吃掉了（对象被回收） 
"; } } $apple = new Fruit(); $apple->setName("大苹果"); $apple->setColor("红色"); echo $apple->showColor(); $clone_apple = $apple; $clone_apple->setName("小苹果"); $clone_apple->setColor("青色"); echo $clone_apple->showColor(); ?>

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上面只是将一个类赋值给另一个类，所以此时内存中仍是一个对象。

<?php class Fruit { private $name = "水果"; private $color = "颜色"; public function setName($name){ $this->name = $name; } public function setColor($color){ $this->color = $color; } function showColor(){ return $this->color.'的'.$this->name."
"; } function __destruct(){ echo "被吃掉了（对象被回收） 
"; } function __clone(){ $this->name = "克隆水果"; } } $apple = new Fruit(); $apple->setName("大苹果"); $apple->setColor("红色"); echo $apple->showColor(); $clone_apple = clone $apple; $clone_apple->setColor("青色"); echo $clone_apple->showColor(); ?>

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clone方法克隆出了一个新的类，所以此时内存中有两个对象。

php的__clone()方法对一个对象实例进行的浅复制,对象内的基本数值类型进行的是传值复制，而对象内的对象型成员变量,如果不重写__clone方法,显式的clone这个对象成员变量的话,这个成员变量就是传引用复制,而不是生成一个新的对象.如下面一个例子的第28行注释所说

<?php 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() { #复制方法,可在里面定义再clone是进行的操作 $this->id = 0; $this->account = clone $this->account; #不加这一句,account在clone是会只被复制引用,其中一个account的balance被修改另一个也同样会被修改 } } $person = new Person("peter", 15, new Account(1000)); $person->setId(1); $person2 = clone $person; $person2->account->balance = 250; var_dump($person, $person2); ?>

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输出:

代码如下:

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) } }