class A {
??? public static function who() {
??? ??? echo __CLASS__;
??? }
??? public static function test() {
??? ??? self::who();
//??? ??? static::who();
??? }
}
A::test();

class B extends A {
??? public static function who() {
??? ??? echo __CLASS__;
??? }
}
echo B::test();

?

如果使用关键字self运行结果：?? A A

如果使用关键字static运行结果：A B

static：父类访问了子类的静态方法

self: 是类内指针，指向本类，静态方法，属性