PHP 魔术方法指的是在某些时刻会自动被调用的内置函数，它们以两个连续的下划线开头。
类中的魔术方法
__construct()
类的构造函数，用于初始化对象，在对象实例化时自动运行
__destruct()
析构函数，用于在 php 运行终止时，释放对象所占用的内存。析构函数是 php 的垃圾回收机制，使用栈结构，后进先出。
构造函数和析构函数的例子
class computer{
private $brand;
function __construct($brand){
$this->brand = $brand;
}
function __destruct(){
echo "release ".$this->brand."<br>";
}
}
$myComputer = new computer("MAC");
$yourComputer = new computer("Asus");
$hisComputer = new computer("Dell");
echo "end of php file<br>";
输出结果如下所示
end of php file release Dell release Asus release MAC
可以发现析构函数在 php 文件执行结束之后才执行
__get($name)
类中用 protected 和 private 关键字定义的成员属性或方法是无法通过对象的实例访问的。__get() 方法会且仅会在对象的实例访问 proctected 和 private 成员属性 时自动执行 (访问成员方法时不会，因为没有意义)。
__get() 方法的意义在于将 proctected 和 private 成员属性进行处理后输出。
__get() 有且仅有一个输入参数
__get() 方法的一个例子
class computer{
private $brand;
protected $owner;
public $price;
function __construct($brand, $owner, $price){
$this->brand = $brand;
$this->owner = $owner;
$this->price = $price;
}
function __get($name){
echo "It‘s up to me to decide if let you konw the owner and the brand of this computer or not :)<br>";
echo "I will tell you the name of woner: ".$this->owner."<br>";
echo "I won‘t tell you that the brand is ".md5($this->brand)."<br>";
echo "<br>";
}
function __destruct(){
echo "release ".$this->brand."<br>";
}
}
$myComputer = new computer("MAC", "me", "1000");
$yourComputer = new computer("Asus", "you", "500");
$hisComputer = new computer("Dell", "his", "700");
echo $myComputer->price;
echo "<br><br>";
echo $myComputer->owner;
echo $yourComputer->brand;
echo "end of php file<br>";
输出如下
1000 It‘s up to me to decide if let you konw the owner and the brand of this computer or not :) I will tell you the name of woner: me I won‘t tell you that the brand is 2e25c285356cbb0ed8785a1377027d79 It‘s up to me to decide if let you konw the owner and the brand of this computer or not :) I will tell you the name of woner: you I won‘t tell you that the brand is cb6ab3315634a1e4d11b091ba48b60ba end of php file release Dell release Asus release MAC
可以看到，当访问 public 成员属性 price 时，__get()方法并没有被调用。输出 brand 时，我们使用了 md5 对其进行了加密处理，这种对封装的成员属性进行处理后输出的用法就是 get 方法的意义所在。
__set($name, $value)
__set($name, $value) 与用于给当前类中封装的方法或属性进行重新赋值或定义。
与 get 类似但不同的时，__set($name, $value)会在成员属性被访问赋值时自动执行，其中 $name 是被访问的成员属性名，$value 为成员属性被赋予的值
__set() 的例子
class computer{
private $brand;
protected $owner;
function __construct($brand, $owner, $price){
$this->brand = $brand;
$this->owner = $owner;
$this->price = $price;
}
function __get($name){
echo "It‘s up to me to decide if let you konw the owner and the brand of this computer or not :)<br>";
echo "I will tell you the name of woner: ".$this->owner."<br>";
echo "I won‘t tell you that the brand is ".md5($this->brand)."<br>";
echo "<br>";
}
function __set($name, $value){
$this->owner = $value;
echo "set $name to $value"."<br><br>";
}
function __destruct(){
echo "release ".$this->brand."<br>";
}
}
$myComputer = new computer("MAC", "me", "1000");
echo $myComputer->owner = "my friend";
echo $myComputer->owner;
echo "end of php file<br>";
输出结果
set owner to my friend my friendIt‘s up to me to decide if let you konw the owner and the brand of this computer or not :) I will tell you the name of woner: my friend I won‘t tell you that the brand is 2e25c285356cbb0ed8785a1377027d79 end of php file release MAC
我们看到在给 owner 赋值时调用了 set , 而访问属性时，调用了 get 。
__tostring()
用于直接打印对象句柄，也就是说当我们使用 echo 加对象名时，__torsring()将会被自动调用
__tosring() 例子
class computer{
function __tostring(){
return "This is a computer class";
}
}
$myComputer = new computer();
echo $myComputer;
如果没有 __totring() 方法，我们是无法使用 echo+对象名，会出现 fatal error
__call($method, $arguments)
当我们调用不存在的方法时，__call() 会自动执行，用于进行异常处理，并使程序继续正常运行。
__call() 例子
class computer{
function start(){
echo "starting computer<br>";
}
function __call($m, $a){
echo "erro function: ".$m;
echo "<br>";
echo "error param: ";
print_r($a);
echo "<br>";
}
}
$myComputer = new computer();
$myComputer->start();
$myComputer->shutdown(‘10 min‘, ‘20 min‘);
echo "here";
输出结果为
starting computer erro function: shutdown error param: Array ( [0] => 10 min [1] => 20 min ) here
我们可以看到，$method 返回了错误的函数名，而 arguments 返回了参数，最后输出了 "here" 说明程序继续正常运行。
__clone() 方法 和 clone 关键字
clone 关键字用于复制对象，__clone() 方法实在克隆对象时自动调用的函数
clone 例子
class computer{
public $name;
function __clone(){
echo "A computer has been cloned<br>";
}
}
$myComputer = new computer();
$youComputer = $myComputer;
$youComputer->name = ‘pc1‘;
echo "My computer‘s name is ".$myComputer->name."<br>";
echo "<br>";
$hisComputer = clone $myComputer;
$hisComputer->name = ‘pc2‘;
echo "My computer‘s name is ".$myComputer->name."<br>";
echo "His computer‘s name is ".$hisComputer->name."<br>";
输出结果
My computer‘s name is pc1 A computer has been cloned My computer‘s name is pc1 His computer‘s name is pc2
我们看到用 = 号并不能复制对象，只是为对象添加了一个别名而已，这里 $myComputer 和 $youComputer 指向同一块内存，修改了 $youComputer 的值相当于修改了 $myComputer 的值。
__autolaod()
在实例化对象时，__autolaod() 会自动被调用，用于快速取得对应的类文件
__autoload() 例子
<?php
function __autoload($class_name) {
include $class_name . ‘.php‘;
}
$obj = new MyClass1();
$obj2 = new MyClass2();
?>
摘自PHP手册
带 try, catch 异常处理的例子
function __autoload($class_name){
echo "want to load ".$class_name."<br>";
if(file_exists($class_name.".class.php")){
include($class_name.".class.php");
}else{
throw new Exception("Unable to laod ".$class_name.".class.php");
}
}
try{
$obj = new myClass();
}
catch(Exception $e){
echo $e->getMessage()."<br>";
}
本文出自 “打个篮球就那么难” 博客，请务必保留此出处http://gipanda.blog.51cto.com/3808693/1423752