1. Comparing things
Comparable & Comparator

2. Maybe we are jumping the gun a bit here
but please live with it for a while.
We are wanting to implement a set of “things” of the same class
obviously 
A set disallows duplicates. So, when we add something to the
set we must make sure it is not already in the set.
Consequently we need to be able to compare “things”.
There are, broadly, 2 ways to do this

3. preliminaries
We are going to use two classes from java.util
TreeSet
HashSet

4. TreeSet

8. HashSet

12. Comparable

13. Comparable
We want to create a set of people (class Person) where
a Person has a first and second name

14. Comparable

15. Comparable

16. Comparable

17. Comparable
It’s comparable

18. Comparable
x.compareTo(y)

19. Comparable

20. Comparable
Duplicate not added

21. Comparable
Same again but Species
rather than Person

22. Comparable
Duplicate avoided

23. Comparator

24. Comparator
We now look at an alternative, the Comparator,
an object that is used to make comparisons
Our example uses cars

25. Comparator

26. Comparator

27. Comparator

28. Comparator

29. Comparator

30. Comparator
Duplicate omitted

32. Comparator

33. Comparator
Why do we get duplicates?

34. HashSet v TreeSet

35. HashSet doesn’t allow us to use Comparable or Comparator
Why?