The Driver class is much simpler. It has one feature, a class method public static void main(String[] args)1. Everything that needs to be done will be done in the main method. A template might be:

public class Driver{
    
   public static void main(String[] args){

   }
    
}
Class vs. Static Features

A class feature belongs to the class, no object is necessary to use it. Examples include math methods we write

double five = Math.sqrt(25.);

to access the class function sqrt(). We do not have to create a Math object first:

Math mo = new Math();       // Incorrect
double five = mo.sqrt(25.); // Incorrect

Java uses the keyword static as a function modifier to create class methods and attributes. Not all languages use the static keyword in the same way. Be careful when using static in discussing class-level features. In Java they are virtually synonymous, but in general they are not.

Accessing the Instance Class

Lets add an instance Ingredient as i1.

public static void main(String[] args){
    Ingredient i1 = new Ingredient();
}
How Does the Compiler Handle User-Defined Classes?

When the java compiler (javac) sees an identifier it does not understand, it looks in

  • the rest of the file being compiled
  • the classes covered by the import statements
  • the directory the .java file is in
    • If it finds a .java file it also compiles it
    • If it finds a .class file it uses it

So when our Driver.java uses Ingredient, the java compiler (re)compiles Ingredient.java.

  1. In Java, class methods have the modifier static ↩︎