public class Library {

    public static void main(String[] a) {

       // variable x is of type int (a built-in)
       int x;
       x = 123;

       // variable y is of type String (a class from the standard library)
       String y;
       y = "Hi there";

       // variable z is of type ''Book'' - a class that I wrote myself - yeah:
       // you heard that wright: I can make my own types!
       Book z;

       // but, wait .... how can I ''assign a value to a Book variable''?
       // my Book class has a title, an author and a pubblication year...
      
       // -> solution: I use a constructor, called using ''new'':
       z = new Book("The Hitchhiker's Guide to the Galaxy", "Douglas Adams", 1978);

       // cool :)

       // now I can use my own methods to deal with ''Book objects'' such as z:

       System.out.println("the copy of " + z.getTitle() + " is available: " + z.isAvailable());

       z.lendTo("Chris");

       System.out.println("the copy of " + z.getTitle() + " is available: " + z.isAvailable());
     
       z.giveBack();
       
       System.out.println("the copy of " + z.getTitle() + " is available: " + z.isAvailable());

    }

}