PHP Static delay statically binding

If you are a lazy programmer, you see the following code may be annoyed     abstract  class u{    } class U1 extends u{  &NBSP;PU Blic static function Create () {     return new U1 ();  }      }   class U2 E Xtends u{   public static function Create () {     return new U2 ();    }}   This code is Regular work is no problem, but a lot of repetitive code can be annoying   I don't want to add a create method to each subclass, and if you put the Create method in superclass U, the code might be     abstract class u{  public The static function create () {   return new self ()  }} class U1 extends u{  function A () {}}   CL Ass U2 extends u{ } u1::create ();   looks neat and tidy, now we put the common code in one place and use self as a reference to that class. But here we make a hypothesis about self.   In effect, self does not have exactly the same effect on the class as $this does on the object. Self refers not to the calling context, he refers to the parsing context, so if you run the above, you will get the   Fatal Error:cannot instantiate abstract class U in D:\wamp\www\test\oop \static.php on line   So self is resolved to define U for create instead of parsing to the U1 class that invokes self.   php5.3 before, there are strict restrictions on this, resulting in a number of clumsy solutions, php5.3 introduced a delayed static bindingSet   and use the keyword  static   static like self, but it refers to the called class instead of the containing class.   In the following example U1::create will generate U1 objects instead of instantiating the U object     Abstract class u{  public static function create () {  &N Bsp;return new Static ();  } class U1 extends u{}   class U2 extends u{ } u1::create ();   Static can be used not only as an instantiation, but also as a call identifier for a static method, or even from a non-static context self,parent         abstract class u{  Private $group;   Public Function __construct () {      $this->group=static::getgroup (),  }   public stat IC function Create () {   return new static ()  }   static function Getgroup () {     re Turn ' default ';  } class U1 extends u{}   class U2 extends u{ static function Getgroup () {   return ' U2 '; &n BSP;} Class U3 extends u2{ } print_r (U1::create ()); Echo ' <br/> '; Print_r (U3::create ());   U1 object ([group:u:private] => default)   U3 object ([GROUP:U:PRIvate] => U2)