method call - empty parameterfield

Why doesn't this run? The superclass and other classes should be ok.
Are there any obvious mistakes?

When I create the object and when I click void main(string []args), BlueJ says ''method call'' empty parameter field in a new window.

Please help, here is the code:

import java.util.*;

public class libraryManager {

    public void main (String [] args) {

      String input =" ";


      ArrayList<Book> books = new ArrayList<Book>();
      ArrayList<CD> cds = new ArrayList<CD>();

            Book book1 = new Book();
            CD cd1 = new CD();

        System.out.println("Welcome to library management system");
        Scanner reader = new Scanner(System.in);

        do{           

            System.out.println("Main menu: ");
            System.out.println(" 1. Add book to the library ");
            System.out.println(" 2. Add CD to the library ");
            System.out.println(" 3. Print items ");
            System.out.println(" 4. Exit ");
            input = reader.nextLine();


             if (input.equals("1")){
                 System.out.println("Input new book: ");
                 input = reader.nextLine();
                 book1.setName(input);
                 books.add(book1); input ="1";

            }

            if (input.equals("2")){
                System.out.println("Input new CD: ");
                input = reader.nextLine();
                cd1.setName(input);
                cds.add(cd1);}

            if (input.equals("3")){

                System.out.println("Library contains:");
                for (int i= 0; i<books.size(); i++){
                    System.out.println("Book: " + books.get(i).getName());
                }
                for (int i = 0; i<cds.size(); i++){
                    System.out.println("CD: " +cds.get(i).getName());
                }

                break;

            }


    }while(!input.equals( "4"));

}
}

This

public void main(String[] args)

is incorrect. It needs to be static like

public static void main(String[] args)

other valid choices (from Wikipedia) are

public static void main(String... args)

or

public static void main(String args[])