int java.lang.Comparable.compareTo(T o)
本对象与参数进行对比。返回为负表示小于，零表示相等，正数表示大于。
Compares this object with the specified object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.
Comparator泛型接口
int StudentComparator.compare(Student o1, Student o2)
