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

To be able to use the single-argument version of Collection.sort() on an ArrayList of A, A should implement the Comparable interface:

public class A implements Comparable {
  ...
  @Override
  int compareTo(A rhs) {
    ...
  }
}