?php

 //检测变量类型，自己用的最多的是is_array()了，其他的几乎没用过

 $array = array(1,9.9,'abc',array(1,2,3),true,null,);

 v(is_bool(111));    //false

 v(is_integer(9.9));    //false

 v(is_double(9.9));    //true

 v(is_string('abc'));    //true

 v(is_null(''));        //false

 v(is_null(null));    //true

 v(is_array($array));    //true

 function v($var){

     var_dump($var);

 }

 ?>

 <?php

 class A{

     public $name = 'a';

     public function say(){

         echo 'I am ',$this->name;

     }

 }

 class B{

     //类型提示

     public function say(A $A){

         return $A->say();

     }

 }

 class C{}

 $A = new A();

 $B = new B();

 $B->say($A);        //I am a

 $B->say(new C());    //报错 Argument 1 passed to B::say() must be an instance of A, instance of C given

 ?>

 <?php

 class A{

     static public $msg='hello';

     static function say(){

         return self::$msg;

     }

 }

 class B extends A{

     static public $msg = 'world';

     static function say(){

         return parent::say().' '.self::$msg;

     }

 }

 echo B::say();        //hello world

 ?>

 <?php

 //类访问，声明时无需$符，且值不可改

 class A{

     const PI = 3.14;

     public function test(){

         //self::PI = 3.15;    //报错

         return self::PI;

     }

 }

 $a = new A();

 echo $a::PI;        //3.14

 echo $a->test();    //3.14

 ?>

 <?php

 abstract class A{

     protected $name;

     public function sing(){

     }

     abstract public function eat();        //以分号结束

 }

 //$a = new A();    //Cannot instantiate abstract class A

 class dog extends A{

     // Class dog contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (A::eat)

 }

 ?>