The Set Interface

Reading Assignment for Oct 20:
The Collection Interface lesson in the Java Tutorial:
http://java.sun.com/docs/books/tutorial/collections/interfaces/collection.html
The Set interface lesson:
http://java.sun.com/docs/books/tutorial/collections/interfaces/set.html


Recall: A set is a collection that does not contain duplicate elements.

• The Set interface extends Collection.
• The Set interface contains no methods other than those inherited from the Collection interface.
• It adds the restriction that no duplicates are permitted.
  

Two implementations of the Set interface in the JDK:

• HashSet - stores its elements in what is called a hash table. This implementation usually provides the best performance. Elements not in order.
  
• TreeSet - stores its elements in a red-black tree. This implementation allows you to order the elements.
  

Note: I do not expect you to be familiar with hash tables and red-black trees.


Example:
Collection coll = new ... ;

// Define a Collection that contains the elements in coll, but without any duplicates
Collection noRepeats = new HashSet(coll);


Exercise: Write a program that takes some words on the command line and prints a list of the words with duplicates removed.

import java.util.*;
public class FindDups
{
    public static void main(String[] args)
    {
          // finish the program

   }
}

Exercise: Write a program that takes words on the command line and prints 2 lists: one list containing all the words that occurred only once, and another list with all the words that occurred more than once. (Use 2 sets and the removeAll() method).

Note: If you used a HashSet, try using a TreeSet. If you used a TreeSet, try your program with a HashSet.