What's a Set?

	Collection with no duplicates (may or may not have order)


Does Set have any methods in addition to those in Collection?

	no new methods are needed


Set Interface

public interface Set extends Collection {
}


Why make a new interface with no methods?
Why not just implement the Collection interface to make a Set?

	classes that implement Set will not allow duplicates



DEMO	(change Collection to Set)


HashSet implements Set
What can you say about the order of an Iterator on a HashSet?

	Iterator on HashSet gives the elements in no particular order



What's a SortedSet?

	Collection that has order but no duplicates
	an Iterator on a SortedSet gives objects in order


DEMO	(change Set to SortedSet)


TreeSet implements SortedSet
What can you say about the order of an Iterator on a TreeSet?

	Iterator on TreeSet gives the elements in compareTo order


Does SortedSet have any methods in addition to those in Set?


SortedSet Interface

public interface SortedSet extends Set {
       Object first();
       Object last();
}



HashSet implements Set
TreeSet also implements Set
Are there any interface-visible differences besides order?

	theoretically HashSet is constant time
	theoretically TreeSet is logN time


DEMO	(compare times for HashSet and TreeSet)



What methods must a class implement to be stored in a Collection?


When should you implement the toString method? Why?

	always


When should you implement the equals method? Why?

	essentially always
	Collection
	List
	Set
	SortedSet
	ArrayList
	LinkedList
	TreeSet
	HashSet

	contains and remove need equals to work


When should you implement the Comparable interface? Why?

	SortedSet
	TreeSet

	the implementation keeps the elements sorted


When should you implement the hashCode method? Why?

	HashSet

	HashSet uses hashCode to organize the placement of its elements
	so they can be added, removed, and found quickly.


What are the rules for implementing hashCode?

	if two objects are ".equals", hashCode must return the same value

	if two objects are not ".equals", hashCode may return different values
	if hashCode returns the same value, HashSet will be less efficient


Classes in the standard java library already implement these methods.


When you write your own classes, you must implement these methods.