Java custom exercise with Collections.sort

I have this class Test

and I have to write code of other classes to pass assertions. What class Test

:

import java.util.*;

public class Test
{
    public static void main(String[] args)
    {
        Book javabook = new Book("Learn Java",150);
        Book cbook = new Book("C",120); 
        Book[] books = new Book[] {javabook, cbook};

        Library lib = new Library(books);
        assert(lib.pages() == 270);

        List l = lib;
        assert(l.size() == 2);

        Collections.sort(l); 

        assert(l.get(0) == cbook);
        assert(l.get(1) == javabook);
    }
}

      

        
        
        
      

    

I started to create Book class, here is my implementation:

public class Book implements Comparable
{
    private String name;
    private int pages;

    public Book(String name, int pages)
    {
        this.name = name;
        this.pages = pages;
    }

    public int getPages()
    {
        return this.pages;
    }

    public int compareTo(Object obj)
    {
        if(this == obj) return 0;
        else
        {
            Book x = (Book) obj;
            return this.pages - x.pages;
        }
    }
}

      

        
        
        
      

    

Then I wrote the Library class:

import java.util.*;

public class Library extends ArrayList
{
    ArrayList a;

    public Library(Book[] b)
    {
        a = new ArrayList(b.length);
        for(int i=0; i<b.length; i++)
        {
            a.add(b[i]);
        }
    }

    public int pages()
    {
        int p = 0;
        for(int i=0; i<a.size(); i++)
        {
            p += ( (Book) a.get(i) ).getPages();
        }   
        return p;
    }

    public int size()
    {
        return a.size();
    }

    public Object get(int i)
    {
        return a.get(i);
    }
}

      

        
        
        
      

    

I think the problem is in the class Library

, it Collections.sort

doesn't seem to work and I cannot pass assertions after calling the sort method on the Test class! I can't figure out what is the problem with my code, can anyone help me?

Remember: I need to make my code to pass assert

s. I'm not sure about my library implementation to make this line in test work:

List l = lib;

      

        
        
        
      

    

Not sure about extending ArrayList.
PS I know it's better to use generic types, but I shouldn't be using them for this exercise. I don't use them, I get some warnings, I just ignore them.