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

<?php
error_reporting(E_ALL);
class test3{
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 $c;
return self::$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 = test3::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 test4
{
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 test5 extends test4
{
// private $private;
public function __construct()
{
parent::tank();
parent::__construct();
//$this->private   = 'private    <br>';
}

public function tank()
{
echo $this->public;
echo $this->private;       //Notice: Undefined property: test5::$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 test5();
$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。