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

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。

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
';
$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，
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。

代码如下:

PHP
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。
?>

从上面的例子中，我们可以看出，
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。

原文地址：https://www.jb51.cc/php/26208.html