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PHP編程中的__clone()方法使用詳解

更新時(shí)間：2015年11月27日 15:40:28 作者：Alexis_Liu

這篇文章主要介紹了PHP編程中的__clone()方法使用詳解,__clone()方法相當(dāng)于一個(gè)淺拷貝,是PHP入門(mén)學(xué)習(xí)中的基礎(chǔ)知識(shí),需要的朋友可以參考下

可以在對(duì)象類(lèi)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(lèi)，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：

<?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 />";
?>

程序運(yùn)行結(jié)果

drone1 employeeID: 12345
drone2 employeeID: 67890
drone2 tiecolor:

再來(lái)一個(gè)小例子：

<?php
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();
?>

上面只是將一個(gè)類(lèi)賦值給另一個(gè)類(lèi)，所以此時(shí)內(nèi)存中仍是一個(gè)對(duì)象。

<?php
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 />"; 
 }
 function __clone(){
 $this->name = "克隆水果"; 
 }
}

$apple = new Fruit();
$apple->setName("大蘋(píng)果");
$apple->setColor("紅色");
echo $apple->showColor();

$clone_apple = clone $apple;
$clone_apple->setColor("青色");

echo $clone_apple->showColor();
?>

clone方法克隆出了一個(gè)新的類(lèi)，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(lèi)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)

<?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() {  #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);
  
 ?>

輸出:

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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