【www.bbyears.com--面向对象编程】
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
error_reporting(E_ALL);
class test{
public $public;
private $private;
protected $protected;
static $instance;
public function __construct(){
$this->public = "public
";
$this->private = "private
";
$this->protected = "protected
";
}
static function tank(){
if (!isset(self::$instance[get_class()]))
{
$c = get_class();
self::$instance = new $c;
}
return self::$instance;
}
public function pub_function() {
echo "you request public function
";
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
";
}
private function pri_function(){
echo "you request private function
";
}
}
$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
?>
public = "public
"; $this->private = "private
"; $this->protected = "protected
"; } static function tank(){ if (!isset(self::$instance[get_class()])) { $c = get_class(); self::$instance = new $c; } return self::$instance; } public function pub_function() { echo "you request public function
"; 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
"; } private function pri_function(){ echo "you request private function
"; } } $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。
class test{
public $public;
private $private;
protected $protected;
static $instance;
public function __construct(){
$this->public = "public
";
$this->private = "private
";
$this->protected = "protected
";
}
protected function tank(){ //私有方法不能继承,换成public,protected
if (!isset(self::$instance[get_class()]))
{
$c = get_class();
self::$instance = new $c;
}
return self::$instance;
}
public function pub_function() {
echo "you request public function
";
echo $this->public;
}
protected function pro_function(){
echo "you request protected function
";
echo $this->protected;
}
private function pri_function(){
echo "you request private function
";
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
";
}
public function pri_extends_function(){
echo "you request extends_private function
";
}
}
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。
?>