No. Any order would work.
Another way to organize the program is to put each class and interface into its own file.
If this is done, each class can be made public.
Put all files into the same subdirectory (folder).
//File: Taxable.java
public interface Taxable
{
}
//File: Goods.java
public class Goods
{
}
//File: Food.java
public class Food extends Goods
{
}
//File: Toy.java
public class Toy extends Goods implements Taxable
{
}
//File: Book.java
public class Book extends Goods implements Taxable
{
}
//File: StoreTester.java
public class StoreTester
{
}
Compile and run in the usual way.
The Java compiler looks for and compiles all the files it needs to compile Store.java.
The interface, also, compiles into a separate file, Taxable.class
C:\Temp>javac StoreTester.java
C:\Temp>java StoreTester
item: bubble bath price: 1.4
item: ox tails price: 4.45
calories: 1500.0
item: Legos price: 54.45
minimum age: 8
Tax is: 3.267
item: Emma price: 24.95
author: Austen
Tax is: 1.4969999999999999
C:\Temp>dir
08/22/2014 07:52 AM 811 Book.class
08/22/2014 07:47 AM 347 Book.java
08/22/2014 07:53 AM 708 Food.class
08/22/2014 07:52 AM 265 Food.java
08/22/2014 07:52 AM 750 Goods.class
08/22/2014 07:46 AM 355 Goods.java
08/22/2014 07:53 AM 1,157 StoreTester.class
08/22/2014 07:44 AM 504 StoreTester.java
08/22/2014 07:52 AM 179 Taxable.class
08/22/2014 07:50 AM 200 Taxable.java
08/22/2014 07:52 AM 825 Toy.class
08/22/2014 07:52 AM 443 Toy.java
12 File(s) 6,544 bytes
C:\Temp>
Which of the two styles (one big file or separate files) would a BlueJ project look like?