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";
}
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()."<br />";
echo "drone2 employeeID: ".$drone2->getEmployeeID()."<br />";
echo "drone2 tiecolor: ".$drone2->getTiecolor()."<br />";
?>
程序运行结果
drone1 employeeID: 12345 drone2 employeeID: 67890 drone2 tiecolor:
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."<br />";
}
function __destruct(){
echo "被吃掉了（对象被回收） <br />";
}
}
$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();
?>
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."<br />";
}
function __destruct(){
echo "被吃掉了（对象被回收） <br />";
}
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();
?>
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);
?>
输出:
复制代码 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) } }