Thread: Implementing basic operations on sets using Array Lists

Hi I'm new to computer science and working on a program to implement a set class using array lists I was looking for some help because I am completely loss right now

import java.util.*;
 
public class Set 
{
    private ArrayList<String> elements;
 
   /**
    * creates an empty set
    */
   public Set()
   {
       elements = null;
   }
 
   /**
    * creates a set using the elements of the ArrayList s.
    * @param s the ArrayList whose elements are used to
    *        create this set.
    * @throws IllegalArgumentException if s contains duplicity.
    */
   public Set(ArrayList<String> s)
   {
       int i;
       elements = new ArrayList<String>();
       for(i=0; i<s.size(); i++)
       {
          if (elements.contains(s.get(i)))
              throw new IllegalArgumentException("Set(ArrayList<String>):duplicity not allowed in sets");
          elements.add(s.get(i));
       }
   }
 
    /**
    * creates a set using the elements of the array s.
    * @param s the array whose elements are used to
    *        create this set.
    * @throws IllegalArgumentException if s contains duplicity.
    */
   public Set(String[] s)
   {
       int i;
       elements = new ArrayList<String>();
       for(i=0; i<s.length; i++)
       {
          if (elements.contains(s[i]))
              throw new IllegalArgumentException("Set(String[]):duplicity not allowed in sets");
          elements.add(s[i]);
       }
   }
 
   /**
    * determines whether a set contains the specified element
    * @param elt an element
    * @return true if elt is an element of this set; otherwise, false
    */
   public boolean isElement(String elt)
   {
       return elements.contains(elt);
   }
 
   /**
    * determines the size of this set.
    * @return the size of this set.
    */
   public int cardinality()
   {
       return elements.size();
   }
 
   /**
    * computes the intersection of this set and the
    * specified set.
    * @param s a set
    * @return a set representing the intersection of this set
    *         and s.
    */
   public Set intersect(Set s)
   {
       int i;
       ArrayList<String> result = new ArrayList<String>();
       for (i=0;i<s.cardinality();i++)
           if (this.isElement(s.elements.get(i)))
               result.add(s.elements.get(i));
       return new Set(result);           
   }
 
   /**
    * computes the union of this set and the specified set.
    * @param s a sets
    * @return a set representing the union of this set
    *         and s.
    */
   public Set union(Set s)
   {
       int i;
       ArrayList<String> result = new ArrayList<String>();
       for (i=0; i<s.cardinality(); i++) 
     {
       if (elements.contains(i))
         result.add(s.elements.get(i));  		  
     }
    return new Set(result);   
   }
 
   /**
    * computes the difference between this set and the
    * specified set.
    * @param s a set
    * @return a set representing the difference between
    *         this set and s.
    */
   public Set diff(Set s)
   {
        int i;
       ArrayList<String> result = new ArrayList<String>();
       for (i=0; i<s.cardinality(); i++) 
     {
       if (elements.contains(i))
         result.remove(s.elements.get(i));  		  
     }
    return new Set(result); 
   }
 
   /**
    * computes the symmetric difference between this set
    * and the specified set.
    * @param s a set
    * @return a set representing the symmetrix difference
    *         between this set and s.
    */
   public Set symDiff(Set s)
   {
       //implement this method     
   }
 
   /**
    * computes the Cartesian product for this set
    * and the specified set.
    * @param s a set
    * @return a set representing the Cartesian product
    *         of this set and s.
    */
   public Set xProduct(Set s)
   {
       //implement this method
   }
 
 
   /**
    * determines whether a set is empty
    * @return true if this set is empty; otherwise, false
    */
   public boolean isEmpty()
   {
       return elements.isEmpty();
   }
 
   /**
    * determines whether this set is equal to the specified
    * set.
    * @param s a set
    * @return true if this set is equal to s; otherwise, false
    */
   public boolean equals(Set s)
   {
       //implement this method
   }
 
   /**
    * determines whether this set is a subset of the specified set.
    * @param s a set
    * @return true if this set is a subset of s; otherwise, false
    */
   public boolean subset(Set s)
   {
       //implement this method
 
   }
 
   /**
    * determines whether this set is a proper subset of the specified set.
    * @param s a set
    * @return true if this set is a proper subset of s; otherwise, false
    */
   public boolean properSubset(Set s)
   {
       //implement this method
   }
 
   /**
    * returns a string {x1,x2,...,xn} representing this set,
    * where x1,x2,...,xn are elements of this set.
    * @return a string representation of this set formatted
    *         as specified.
    */
   public String toString()
   {
       //implement this method            
   } 
}

this is what I have so far currently I'm stuck on sym diff

Originally Posted by Bucs1992

this is what I have so far currently I'm stuck on sym diff

Hello Bucs!
Where are you stuck? Can you explain what you are trying to do and is not working? Do you have the logic for the method?
The symmetric difference can be expressed as the union without the intersection and as I can see you have implemented union and intersection.