php 面向对象访问控制 public,private,protected详解
文章利用举例说明了关于PHP5面向对象访问控制 Public,private,protected详细说明，有需要的朋友可以参考一下。在PHP5中增强了面向对象的机制，加入了面向对象常见的public、private、protected这样的访问控制机制。从字面意思来理解：
Public 无疑是公共的意思，意思是说类本身和其外部的子类都可以访问这个属性或者方法；
Private 英文翻译过来就是私有的意思，只能是类本身在类的内部才能访问——实例化的对象句柄不能访问该属性和方法，子类也不能访问；
Protected 受保护的属性或者方法，这个属性或者是方法只能被类本身或者子类的内部访问，实例化的对象句柄不能访问。
现在我们举个例子来说这个问题。
假设有一个宝石博物馆的管理员 小李，把仓库中的宝石分为三个类别，红宝石，蓝宝石，绿宝石。并且划分了属性，红宝石是国家的任何人都可以参观标签为（public），蓝宝石管理员小李家族传下来的（protected），绿宝石是小李自己在山上见到的（private）。
那么我们可以这样认为：
public标签的红宝石，是国家的——全民所有，只要是合法的国家的公民都能够参看和拍照。
Protected 这个是受保护的，只有小李家族的人（小李的孩子或者孙子）在特定的房间里面才能参观和拍照，不准拿到房间外边看——太小气了！
Private 这个是私有的，小李不想让其他人知道，更不想让拍照了，所以只能供小李在小李的房间里看看而已，其他的人即使小李的孩子们都没有办法看到
实例
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<?php error_reporting(E_ALL);
class test{ public $public; private $private; protected $protected; static $instance; public function __construct(){ $this->public = 'public <br>'; $this->private = 'private <br>'; $this->protected = 'protected <br>'; } static function tank(){ if (!isset(self::$instance[get_class()])) { $c = get_class(); self::$instance = new $c; }
return self::$instance; }
public function pub_function() { echo "you request public function<br>"; echo $this->public; echo $this->private; //private,内部可以调用 echo $this->protected; //protected,内部可以调用 $this->pri_function(); //private方法，内部可以调用 $this->pro_function(); //protected方法，内部可以调用 } protected function pro_function(){ echo "you request protected function<br>"; } private function pri_function(){ echo "you request private function<br>"; } }
$test = test::tank(); echo $test->public; echo $test->private; //Fatal error: Cannot access private property test::$private echo $test->protected; //Fatal error: Cannot access protected property test::$protected $test->pub_function(); $test->pro_function(); //Fatal error: Call to protected method test::pro_function() from context $test->pri_function(); //Fatal error: Call to private method test::pri_function() from context
?>
<?php error_reporting(E_ALL); class test{ public $public; private $private; protected $protected; static $instance; public function __construct(){ $this->public = 'public <br>'; $this->private = 'private <br>'; $this->protected = 'protected <br>'; } static function tank(){ if (!isset(self::$instance[get_class()])) { $c = get_class(); self::$instance = new $c; } return self::$instance; } public function pub_function() { echo "you request public function<br>"; echo $this->public; echo $this->private; //private,内部可以调用 echo $this->protected; //protected,内部可以调用 $this->pri_function(); //private方法，内部可以调用 $this->pro_function(); //protected方法，内部可以调用 } protected function pro_function(){ echo "you request protected function<br>"; } private function pri_function(){ echo "you request private function<br>"; } } $test = test::tank(); echo $test->public; echo $test->private; //Fatal error: Cannot access private property test::$private echo $test->protected; //Fatal error: Cannot access protected property test::$protected $test->pub_function(); $test->pro_function(); //Fatal error: Call to protected method test::pro_function() from context $test->pri_function(); //Fatal error: Call to private method test::pri_function() from context ?> 从上面的例子中，我们可以看出， <?php
class test{ public $public; private $private; protected $protected; static $instance;
public function __construct(){ $this->public = 'public <br>'; $this->private = 'private <br>'; $this->protected = 'protected <br>'; } protected function tank(){ //私有方法不能继承，换成public,protected if (!isset(self::$instance[get_class()])) { $c = get_class(); self::$instance = new $c; } return self::$instance; }
public function pub_function() { echo "you request public function<br>"; echo $this->public; } protected function pro_function(){ echo "you request protected function<br>"; echo $this->protected; } private function pri_function(){ echo "you request private function<br>"; echo $this->private; } }
class test1 extends test{
public function __construct(){ parent::tank(); parent::__construct(); } public function tank(){ echo $this->public; echo $this->private; //Notice: Undefined property: test1::$private echo $this->protected; $this->pub_function(); $this->pro_function(); $this->pri_function(); //Fatal error: Call to private method test::pri_function() from context 'test1' }
public function pro_extends_function(){ echo "you request extends_protected function<br>"; } public function pri_extends_function(){ echo "you request extends_private function<br>"; } }
error_reporting(E_ALL); $test = new test1(); $test -> tank(); //子类和父类有相同名字的属性和方法，实例化子类时，子类的中的属性和方法会盖掉父类的。
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