Collections.sort() error

Question

I am trying to sort a list of type A named BinOrder in class B according to Class A\'s int r.

However i am receiving this error for the line Collections.sort(BinOrder);<

Answer 1

Here's the signature of Collections.sort :

public static > void sort(List list)

A must implement Comparable for this method.

You try to pass BinOrder to this method, when BinOrder is of type ArrayList, but since A does not implement Comparable, it doesn't fit the signature of the method.

Either change A to implement Comparable, or use the sort method that accepts a Comparator :

public static  void sort(List list, Comparator c)