PHP类继承，相关构造函数

header("Content-Type:text/html;charset=utf-8");<br /><br />class Class1 extends Class2{<br />    public static $a = 'Class1';<br />}<br />class Class2 extends Class3{<br />    public static $a = 'Class2';<br />    public function __construct(){<br />        echo 'Class2';<br />    }<br />}<br />class Class3{<br />    public static $a = 'Class3';<br />    public function __construct(){<br />        echo 'Class3';<br />    }<br />}<br /><br />$obj = new Class1();<br />