Re: casting class to interface

I get an exception ("ClassCastException") when I try to cast Resource
to Comparable2... any idea why?

// Resource.java

class Resource
{

    private String title, firstName, lastName, publisher, dateOfEdition,
ISBN, libraryCallNumber;
    private int numberOfPages, editionNumber;

    Resource(String title,String ISBN,String libraryCallNumber,String
publisher, String firstName,
        String lastName, int editionNumber,String dateOfEdition,int
numberOfPages)
    {
        this.title = title;
        this.ISBN = ISBN;
        this.libraryCallNumber = libraryCallNumber;
        this.publisher = publisher;
        this.firstName = firstName;
        this.lastName = lastName;
        this.editionNumber = editionNumber;
        this.dateOfEdition = dateOfEdition;
        this.numberOfPages = numberOfPages;
    }

    public String toStringLong()
    {
        return " Title: " + title + "\n"
             + " ISBN: " + ISBN + "\n"
             + " Library Call Number: " + libraryCallNumber + "\n"
             + " Publisher: " + publisher + "\n"
             + " Author: " + firstName + " " + lastName +
"\n"
             + " Edition Number: " + editionNumber + "\n"
             + " Date of Edition: " + dateOfEdition + "\n"
             + " Number of Pages: " + numberOfPages + "\n";
    }

    public String toString() {
        return title + " - " + firstName + " " + lastName;
    }

    public String toStringEncoded() {
        final String glue = ";";
        return title + glue + ISBN + glue + libraryCallNumber + glue +
publisher + glue + firstName + glue
            + lastName + glue + editionNumber + glue + dateOfEdition + glue +
numberOfPages + "\n";
    }

    public String toString1() {
        return lastName + firstName + title + editionNumber + publisher;
    }

    public String toString2() {
        return title + editionNumber + publisher + lastName + firstName;
    }

    public int compareTo1(Comparable2 obj) {
        return toString1().compareToIgnoreCase(obj.toString1());
    }

    public int compareTo2(Comparable2 obj) {
        return toString2().compareToIgnoreCase(obj.toString2());
    }
}

// Comparable2.java

public interface Comparable2
{
    public String toString1();
    public String toString2();

    public int compareTo1( Comparable2 obj );
    public int compareTo2( Comparable2 obj );

}