Problem applying Generics

[adam smith ii]

In Java tutorial, exercise is:
Design a class that acts as a library for the following kinds of media: book, video, and newspaper. Provide one version of the class that uses generics and one that does not. Feel free to use any additional APIs for storing and retrieving the media.

import java.util.ArrayList;

/*
 * example of using Generics
 */

public class Library<T> {

    private ArrayList<T> mediaCollection = new ArrayList<T>();

    public Library() {
        Book b = new Book();
        storeMedia(b);
        Video v = new Video();
        storeMedia(v);
        Newspaper n = new Newspaper();
        storeMedia(n);
        showMedia();
    }

    public void showMedia() {
        System.out.println("These items are in the media collection:");
        for (Object resource : mediaCollection.toArray()) {
            System.out.print("\t" + resource.toString() + "\n");
        }
    }

    public void storeMedia(T item) {
        mediaCollection.add(item);
    }

    public class Book implements Media {

        String type = "book";
        String name = "Robinson Curuso";

        public Book(){
            System.out.println(this.getClass());
        }

        public String toString() {
            return "type is " + type + ", name is: " + name;
        }
    }

    class Video implements Media {

        String type = "video";
        String name = "Elvis Pressley in the Army";

        public String toString() {
            return "type is " + type + ", name is: " + name;
        }
    }

    class Newspaper {

        String type = "newspaper";
        String name = "News & Disturber";

        public String toString() {
            return "type is " + type + ", name is: " + name;
        }
    }

    interface Media {
//        String type;
    }

    public static void main(String[] args) {
        Library<Media> lib = new Library<Media>();
    }

}
    

Current error is on line 13 the "storeMedia(b);" and other two similar lines. Error message, "method storeMedia in class Library<T> cannot be applied to given types, required T, found Library<T>.Book.

I have made many attempts trying to get clean compile. I think I am missing a basic concept so an explanation along with the code remedy would be appreciated. Thanks in advance.

[steve claflin]

I think the problem is that you have defined Media and the implementing classes as inner classes of Library. Even though the class is parameterized with T, you are locking in within the class what T must be. One solution would be to move Media and the implementing classes outside of Library. Another approach would be to have Library not be parameterized, and to make the ArrayList field be ArrayList<Media>, which is what I think the intent of the exercise is.

Also note that your Newspaper does not implement Media.