Object-Oriented Design - Java Software Solutions: Foundations of Program Design - page 307

Because static methods do not operate in the context of a particular object,
they cannot reference instance variables, which exist only in an instance of a class.
The compiler will issue an error if a static method attempts to use a nonstatic
variable. A static method can, however, reference static variables, because static
variables exist independent of specific objects. Therefore, the main method can
access only static or local variables.
The program in Listing 7.1 instantiates several objects of the Slogan class,
printing each one out in turn. At the end of the program it invokes a method
called getCount through the class name, which returns the number of Slogan
objects that were instantiated in the program.
LISTING 7.1
//********************************************************************
// SloganCounter.java Author: Lewis/Loftus
//
// Demonstrates the use of the static modifier.
//********************************************************************
public class SloganCounter
{
//-----------------------------------------------------------------
// Creates several Slogan objects and prints the number of
// objects that were created.
//-----------------------------------------------------------------
public static void main (String[] args)
{
Slogan obj;
obj = new Slogan ("Remember the Alamo.");
System.out.println (obj);
obj = new Slogan ("Don't Worry. Be Happy.");
System.out.println (obj);
obj = new Slogan ("Live Free or Die.");
System.out.println (obj);
obj = new Slogan ("Talk is Cheap.");
System.out.println (obj);
obj = new Slogan ("Write Once, Run Anywhere.");
System.out.println (obj);