class person implements Comparable<person>
{
    public String name;
    public int compareTo(person x) {return name.compareTo(x.name);}
}

class student extends person implements Comparable<person>
{
    public double gpa;
    // boring stuff skipped

    // How is the compareTo method be inherited?
}

//class Sorter<T extends Comparable<T>> // older form
class Sorter<T extends Comparable<? super T>> // since jdk 1.8 
{
    void bubblesort(T[] A) // bubble sorts (pointer to) array A 
    {
        for(int i=0;i<A.length-1;i++)
            for(int k=0;i<A.length-1;k++)
                if (A[k].compareTo(A[k+1])>0) {
                    T tmp = A[k]; A[k]=A[k+1]; A[k+1]=tmp; //swap
                }// not efficient but that's not the point here
    }//bubblesort
    
    static void notreallymain()
    {
	Sorter<student> S = new Sorter<student>(); //compiles with ? super T
	//Sorter<person> S = new Sorter<student>(); //classes never covariant
    }   
}


// what if I try to do a super on a return type?  -- following won't compile
/*
interface D<T>
{
   T f();
}
class DD implements D<person>
{
    public person f() { return null; }
}
class CC<T extends D<? super T>>
{
    static void stillnotmain()
    {
	CC<student> x = new CC<student>();
    }
}
*/