php - 在PHP中，我们如何获取父类变量？

Question

我的印象是子类继承其父类的属性。然而，以下是类 B 中的输出 null...有人能告诉我如何从父类访问属性吗？

$aClass = new A();
$aClass->init();

class A {

    function init() 
    {
        $this->something = 'thing';
        echo $this->something; // thing
        $bClass = new B();
        $bClass->init();
    }

}

class B extends A {

    function init() 
    {
        echo $this->something; // null - why isn't it "thing"?
    }
}

Answer 1

您的代码中有几个错误。我已经纠正它们了。以下脚本应该按预期工作。我希望代码注释对您有所帮助:

class A {

    // even if it is not required you should declare class members
    protected $something;

    function init() 
    {
        $this->something = 'thing';
        echo 'A::init(): ' . $this->something; // thing
    }

}

// B extends A, not A extends B
class B extends A {

    function init() 
    {
        // call parent method to initialize $something
        // otherwise init() would just being overwritten
        parent::init();
        echo 'B::init() ' . $this->something; // "thing"
    }
}


// use class after(!) definition
$aClass = new B(); // initialize an instance of B (not A)
$aClass->init();