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Home Backend Development PHP Tutorial 继承会拥有父类的 Private 属性和方法吗?

继承会拥有父类的 Private 属性和方法吗?

Jun 06, 2016 pm 08:32 PM
php private inherit

看了PHP官方手册,也是“言简意赅”... 属性定义也直接是 var,这阿斗也是醉了,唉...

这里有个帖子,附上了测试的代码:http://bbs.phpchina.com/thread-116668-1-1.html

那到底继承会不会拥有父类的 private 属性和方法呢?继承在意义上来说是不是相当于父类简单的代码拷贝?是不是说子类也会有父类的 private,只是父类的 private 只能父类自己的方法访问,子类的 private 只能子类自己的方法访问?其实各自的 private 还是各自的?

回复内容:

看了PHP官方手册,也是“言简意赅”... 属性定义也直接是 var,这阿斗也是醉了,唉...

这里有个帖子,附上了测试的代码:http://bbs.phpchina.com/thread-116668-1-1.html

那到底继承会不会拥有父类的 private 属性和方法呢?继承在意义上来说是不是相当于父类简单的代码拷贝?是不是说子类也会有父类的 private,只是父类的 private 只能父类自己的方法访问,子类的 private 只能子类自己的方法访问?其实各自的 private 还是各自的?

必须明确:private, publicprotected这几个关键字,和继承一毛钱的关系都没有。人家叫做“可见性(Visibility)”。基类不能控制自己的所有成员都被子类继承走,但可以约束某些被继承的的成员,对子类新增补的成员不可见

从“拥有”这个角度来说,子类是基类的套壳,基类的一切当然都在子类中“存在”——只是从子类的角度能不能“看得到”而已。

如下图(蓝色箭头部分),private member肯定存在在子类的存储空间中,也就是说肯定被子类继承到了。但子类新增的方法就是访问不到。

继承会拥有父类的 Private 属性和方法吗?

这个事情从架构设计这个意义上,其实是很容易说清楚的。一个子类必须遵守基类的所有特征,然后在其上做出增补和扩充。而如果基类的所有成员都开放给子类随便看、随便改,基类的本来特征可以随便拆掉,那么还要继承做什么呢?

在实际工程中,基类的私有成员,要么是基类自己内部使用,要么是像上图(红色箭头部分)一样,通过protected方法做一个访问器,保证既把访问权间接开放给子类,又能在子类访问时执行一些必要的控制逻辑。

当然不会,后面接力。

我感觉继承 应该是向上查找个一个过程, 当我们需要访问一个类中的属性, 首先会看当前类有没有, 若没有就到它的父类中查询! var_dump()打印一个子类的时候是可以看到父类的私有属性, 但是不能访问

可以参考此链接访问控制(可见性),在此贴上部分讲解此问题的文字。关键部分已加粗

对属性或方法的访问控制,是通过在前面添加关键字 public(公有),protected(受保护)或 private(私有)来实现的。
被定义为公有的类成员可以在任何地方被访问。被定义为受保护的类成员则可以被其自身以及其子类和父类访问。被定义为私有的类成员则只能被其定义所在的类访问。

Example #1 属性声明

<code><?php /**
 * Define MyClass
 */
class MyClass
{
    public $public = 'Public';
    protected $protected = 'Protected';
    private $private = 'Private';

    function printHello()
    {
        echo $this->public;
        echo $this->protected;
        echo $this->private;
    }
}

$obj = new MyClass();
echo $obj->public; // 这行能被正常执行
echo $obj->protected; // 这行会产生一个致命错误
echo $obj->private; // 这行也会产生一个致命错误
$obj->printHello(); // 输出 Public、Protected 和 Private


/**
 * Define MyClass2
 */
class MyClass2 extends MyClass
{
    // 可以对 public 和 protected 进行重定义,但 private 而不能
    protected $protected = 'Protected2';

    function printHello()
    {
        echo $this->public;
        echo $this->protected;
        echo $this->private;
    }
}

$obj2 = new MyClass2();
echo $obj2->public; // 这行能被正常执行
echo $obj2->private; // 未定义 private
echo $obj2->protected; // 这行会产生一个致命错误
$obj2->printHello(); // 输出 Public、Protected2 和 Undefined

?></code>
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Example #2 方法声明

<code><?php /**
 * Define MyClass
 */
class MyClass
{
    // 声明一个公有的构造函数
    public function __construct() { }

    // 声明一个公有的方法
    public function MyPublic() { }

    // 声明一个受保护的方法
    protected function MyProtected() { }

    // 声明一个私有的方法
    private function MyPrivate() { }

    // 此方法为公有
    function Foo()
    {
        $this->MyPublic();
        $this->MyProtected();
        $this->MyPrivate();
    }
}

$myclass = new MyClass;
$myclass->MyPublic(); // 这行能被正常执行
$myclass->MyProtected(); // 这行会产生一个致命错误
$myclass->MyPrivate(); // 这行会产生一个致命错误
$myclass->Foo(); // 公有,受保护,私有都可以执行


/**
 * Define MyClass2
 */
class MyClass2 extends MyClass
{
    // 此方法为公有
    function Foo2()
    {
        $this->MyPublic();
        $this->MyProtected();
        $this->MyPrivate(); // 这行会产生一个致命错误
    }
}

$myclass2 = new MyClass2;
$myclass2->MyPublic(); // 这行能被正常执行
$myclass2->Foo2(); // 公有的和受保护的都可执行,但私有的不行

class Bar 
{
    public function test() {
        $this->testPrivate();
        $this->testPublic();
    }

    public function testPublic() {
        echo "Bar::testPublic\n";
    }
    
    private function testPrivate() {
        echo "Bar::testPrivate\n";
    }
}

class Foo extends Bar 
{
    public function testPublic() {
        echo "Foo::testPublic\n";
    }
    
    private function testPrivate() {
        echo "Foo::testPrivate\n";
    }
}

$myFoo = new foo();
$myFoo->test(); // Bar::testPrivate 
                // Foo::testPublic
?></code>
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