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
实例代码如下:
<?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,
public : 可以 class 内部调用,可以实例化调用.
private : 可以 class 内部调用,实例化调用报错.
protected : 可以 class 内部调用,实例化调用报错.
<?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.
?>
