php class中public,private,protected的区别，以及实例-优快云博客

本文链接：https://blog.youkuaiyun.com/hudeyong926/article/details/99540496

本文详细解析PHP中的public, private, protected三种访问修饰符的使用方式及区别，通过实例展示了它们如何影响类成员的可见性和继承性。同时，通过对比分析，说明了不同修饰符对类成员的访问限制和继承的影响。

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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 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。

?>

从上面的例子中，我们可以看出，