CpSc 210, Section 1
                             Assignment 5 
                           February 19, 2002 


Due:  Wednesday, February 27  at 11:59 p.m.  

Assignment:  Implementing a class Set


Total point value of assignment:  100 points
Not accepted late.

This assignment is to be done INDIVIDUALLY.

Assignment:  Design and implement a class, Set, which must be stored in a
     file named Set.java.  (Failure to name file or class correctly is an
     automatic 20 point deduction.)  Mathematically, a set is a collection
     of objects without duplicates and without order (so we shall not
     allow the compareTo method to be used on items in a Set).

     The Set is to be implemented using a Vector as instance variable
     to hold the elements of the Set.  The following methods are required.

     public Set ( )
     // Default constructor, constructs an empty Set

     public void addItem ( Object item )
     // Pre:  item is not null
     // Post:  If item is not in this Set, item is added to this Set.
     //        If item is already in this Set, this Set remains unchanged.

     public boolean contains ( Object item )
     // Pre:  item is not null
     // Post:  returns true if item is in Set.  Otherwise, returns false.

     public boolean isEmpty ( )
     // Post:  returns true if this Set is empty.  Otherwise, returns false.

     public void removeItem ( Object item )
     // Pre:  item is in this Set
     // Post:  item has been removed from this Set

     public int size ( )
     // Post:  returns the number of items in this Set

     public String toString ( )
     // Post:  returns String representation of Set in the form
     //        { elt1, elt2, elt3, ... }   
     //       That is, enclose elements between braces and separate with commas

     public boolean equals ( Object other )
     // Pre:  other is not null and other is a Set
     // Post:  returns true if this and other contain the same collection
     //        of Objects.  Otherwise, returns false.

     public Set union ( Set other )
     // Pre:  other is a Set and is not null (other may be empty)
     // Post:  returns the union of Sets this and other

     public Set intersection ( Set other )
     // Pre:  other is a Set and is not null (other may be empty)
     // Post:  returns the intersection of Sets this and other

     You may include any additional methods you need.  Additional methods
     should be private instead of public.

     Use the instanceof operator to test that other is a Set in the
     equals method.  

         if ( ! ( other instanceof Set ) )  throw new IllegalArgumentException
            ("Argument to equals method must be a set.");            

	You should follow that test with a statement that casts other to a Set,
	such as

	     Set otherSet = (Set) other;

	Then, your code should methods should work with otherSet, instead of other.         
            

 	Sample results are:
	Let A = { 1, 2, 3, 4 }, let B = { 5, 6, 7 }, and let C = { 4, 5 },
         the size of Set A is 4, the size of Set B is 3, and the size of C is 2
         A union B is { 1, 2, 3, 4, 5, 6, 7 }
         A union C is { 1, 2, 3, 4, 5 }
         A intersect B is the empty set
         A intersect C is { 4 }


Grading Rubric:

	 5 pts. reasonable attempt to solve problem as assigned
	10 pts. also compiles
	 5 pts. style standards (includes clarity)

         5 pts. addElement method
         5 pts. contains method
         5 pts. isEmpty method
         5 pts. removeItem method
         5 pts. size method
         5 pts. toString method
         5 pts. equals method
        20 pts. intersection method
   	20 pts. union method

        5 pts. elegance of code