<? super String>与<? ext

super和extends从字面上来说的话是父类引用和子类继承的关系，所以如下所示：

（1）is any class which is as uper class of String(including String itself). (In this case, the only other suitable class isObject.)

即包括String的父类和它本身的String类。

（2）(which in this specific case wouldn't be very useful as Stringis final, so it can have no subclasses).

即包括String的子类，而String没有子类，为null。