public abstract class DataElement
{
    public abstract boolean equals(DataElement otherElement);
      //Method to determine whether two objects contain the 
      //same data.
      //Postcondition: Returns true if this object contains the 
      //               same data as the object otherElement;
      //               otherwise, it returns false.
      
    public abstract int compareTo(DataElement otherElement);
      //Method to compare two objects.
      //Postcondition: Returns a value < 0 if this object is 
      //                    less than the object otherElement;
      //               Returns 0 if this object is the same as 
      //                    the object otherElement.
      //               Returns a value > 0 if this object is 
      //                  greater than the object otherElement.
      
    public abstract void makeCopy(DataElement otherElement);
      //Method to copy otherElement into this object.
      //Postcondition: The data of otherElement is copied into
      //               this object.
      
    public abstract DataElement getCopy();
      //Method to return a copy of this object.
      //Postcondition: A copy of this object is created and
      //               a reference of the copy is returned.
}