关于php类静态变量的例子

example:<?phpclass Example{ static $num=0; function __construct(){ }}class Children extends Example{ function __construct(){ self::$num+=1; }}class Childrentwo extends Example{function ob(){echo self::$num;}}$obj2=new Childrentwo();echo 'result1:'.$obj2->ob();//output: result1:0$obj=new Children();//echo $obj->$num,'<br/>';实例化->读取静态变量无效echo "result2:".$obj::$num.'<br/>';//output: result2:1echo "result3:".Example::$num.'<br/>';//output: result3:1?>