Java Reference
In-Depth Information
On the Web
The listed sample header above is contained in the Chapter 2 folder at
www.crcpress.com
.
ThenameofthefileisHeader.java
The HelloJava code
Let's examine the HelloJava program line-by-line. The program is re-listed be-
low:
// Java version of the Hello World program
// Developed for the topic “Java for Engineers”
// by CRC Press
public class HelloJava
{
public static void main(String[] args)
{
System.out.println(“Hello World, this is Java”);
}
}
The first three program lines are as follows:
//
Java version of the Hello World program
//
Developed for the topic “Java for Engineers”
//
by CRC Press
These three program lines are a comment. They are ignored by the com-
piler and have no other purpose than to document and explain the code. We
have used the // symbol to comment the lines individually.
The first non-comment line of the HelloJava program is as follows:
public class HelloJava
{
Programming languages, Java included, use special language elements
called
keywords
. Keywords are reserved and cannot be used in regular ex-
pressions. The keyword
public
, called an
access modifier
, determines if
other parts of the program can use this code. The keyword
class
is neces-
sary because everything in a Java program exists in a class.
The first class in a Java program is called the
driving class.
The driving
class must have the same name as the file in which it is stored. In other words,
if you save a Java program in a file named MyHello.java, then the driving class
must have the name MyHello. In the sample program, the source file has the
filename HelloJava.java, and the driving class is named HelloJava.
