php class中public,private,protected的区别，以及实例

一，public,private,protected的区别

public:权限是最大的，可以内部调用，实例调用等。

protected: 受保护类型，用于本类和继承类调用。

private: 私有类型，只有在本类中使用。

二，实例
查看复制打印?

    <?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。
查看复制打印?

    <?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。  

    ?>  

从上面的例子中，我们可以看出，
public:    test中的public可以被继承。
private:   test中的private不可以被继承。
protected：  test中的protected可以被继承。
static：        test中的static可以被继承。

唉，对于这些东西，老是不喜欢记着，用的时候，总感觉不对，又要去查，所以写个例子，方便自己查看。