Fundamentals - SCJP Sun Certified Programmer for Java Platform SE6 - page 12

Running Java Applications
The SCJP certifi cation exam tests your knowledge of running a Java program from the
command line using an appropriate CLASSPATH . If you are using Sun's Java Development Kit
(JDK), then java.exe in the \bin folder of the JDK directory is the executable used to run
your Java applications. The sample commands in this topic assume java.exe is in your path.
The entry point of a Java program is main , which you can defi ne in any class. The
signature of main must look like this:
public static void main(String [] args)
The only changes you can make to this signature are the name of the parameter args ,
which can be arbitrary, and the order of public and static . For example, the following
declaration is a valid signature of main :
static public void main(String [] x)
In addition, you can specify the array of String objects using the syntax for variable-
length arguments:
public static void main(String... args)
Variable-Length Arguments
As of Java 5.0, a method in Java can declare a variable-length argument list denoted by
the ellipsis ( ... ). Variable-length arguments are discussed in detail in Chapter 2.
The args array contains the command-line arguments, discussed in detail later in this
section. The main method has to be public so that the JVM has access to it, and making it
static allows the JVM to invoke this method without having to instantiate an instance of
the containing class.
Let's start with a simple example. Suppose the following class is saved in the
c:\myproject directory. First, does the following SaySomething class compile, and does it
successfully declare the main method?
1. public class SaySomething {
2. private static String message = “Hello!”;
3.
4. public static void main() {
5. System.out.println(message);
6. }
7. }