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) } }