Java Comparator using .reverseOrder() but with an inner class

Question

I am creating a simple program to learn about the Java Comparator class. I have sorted an Arraylist into order but now I want to sort the list in descending order b

Answer 1

One way to implement an reverse order comparator is to implement an Compartor-Delegate that invert the comparator result (by changing the order).

public class ReverseOrder implements Comparator {
  private Comparator delegate;
  public ReverseOrder(Comparator delegate){
    this.delegate = delegate;
  }

  public int compare(T a, T b) {
    //reverse order of a and b!!!
    return this.delegate.compare(b,a);
  }
}

So the only thing you need to do is to use this delegate. For example:

  Comparator myComparator = new myComparator();
  List list = ...;
  List reverse = new ArrayList(list);

  //acceding
  Collections.sort(list, myComparator);

  //descending
  Collections.sort(list, new ReverseOrder(myComparator));