php中抽象类在其方法中例化其子类来完成对自己方法的调用

<code><span>abstract</span><span><span>class</span><span>A</span>
{</span><span>private</span><span>static</span><span>$c</span>;
    <span>final</span><span><span>function</span><span>todo</span><span>()</span>
    {</span><span>//do something</span>
    }
    <span>public</span><span><span>function</span><span>init</span><span>()</span>
    {</span><span>$c</span> = <span>new</span> B;
    }
    <span>public</span><span><span>function</span><span>get</span><span>()</span>
    {</span><span>$c</span>->todo();
    }
}
<span><span>class</span><span>B</span><span>extends</span><span>A</span>
{</span>}
....
A::get();</code>