Download public static void main(String args[ ])

CPRG 215
Introduction to
Object-Oriented Programming with Java
Module 1-Introduction to Java
Topic 1.3
Write Your First Java Program
Produced by Harvey Peters, 2008
Copyright SAIT
Please read the following sections
in your textbook
Core Java, Volume I–Fundamentals, Eighth Edition
By Cay S. Horstmann & Gary Cornell
•Chapter 3 - Fundamental Programming Structures
in Java
•A Simple Java Program
•Comments
CPRG 215 Module 1.2- Getting the Tools and Setting Up the Development Machine
Copyright SAIT
A simple Java program
//
// Sample
public class HelloWorldApp
{
public static void main (String args[ ])
{
System.out.println (“Hello World!”);
}
}
CPRG 215 Module 1.3- Write Your First Java Program
Copyright SAIT
Topic 1.3.1
A simple Java program
• //
//Sample
– Comments, not processed by Java
• public class HelloWorldApp
//
// Sample
public class HelloWorldApp
{
public static void main (String args[ ])
{
System.out.println (“Hello World!”);
}
}
– Defines this as a “class”
– Every program in Java is a class
– A class is like a template or blueprint that
defines how an object should be built
CPRG 215 Module 1.3- Write Your First Java Program
Copyright SAIT
Topic 1.3.1
A simple Java program
• {
}
– Code braces that group code
statements together
//
// Sample
public class HelloWorldApp
{
public static void main (String args[ ])
{
System.out.println (“Hello World!”);
}
}
CPRG 215 Module 1.3- Write Your First Java Program
Copyright SAIT
Topic 1.3.1
A simple Java program
• public static void main(String args[ ])
//
// Sample
public class HelloWorldApp
{
public static void main (String args[ ])
{
System.out.println (“Hello World!”);
}
}
– Definition for the main method
– A class must have a main method in order to
run
– If you run a class that has no main method
this message is displayed:
• Exception in thread "main"
java.lang.NoSuchMethodError: main
CPRG 215 Module 1.3- Write Your First Java Program
Copyright SAIT
Topic 1.3.1
A simple Java program
• public static void main(String args[ ])
• public
– access permission - most accessible level
• static
– Able to run as soon as class loads into JVM
– Normally methods don’t exist until we create an
object from the class
• void
– The method does not return any data
• (String args[])
– main receives a String array with command-line
arguments is any are found
CPRG 215 Module 1.3- Write Your First Java Program
Copyright SAIT
Topic 1.3.1
Compiling and running
• Compiling:
– javac HelloWorldApp.java
• Running
– java HelloWorldApp
CPRG 215 Module 1.3- Write Your First Java Program
Copyright SAIT
Topic 1.3.2
Compiling and running
• Troubleshooting
–
–
–
–
–
bad command -- path
file not found -- typo?
Class not found -- forgot to compile?
Method not found -- typo? Case sensitivity
javac: invalid argument -- forgot .java
CPRG 215 Module 1.3- Write Your First Java Program
Copyright SAIT
Topic 1.3.2
Documentation
• Comments
//
/* */
• Javadoc
/***/
CPRG 215 Module 1.3- Write Your First Java Program
Copyright SAIT
Topic 1.3.3
Documentation
• Comments
//
/* */
• Javadoc
/***/
CPRG 215 Module 1.3- Write Your First Java Program
Copyright SAIT
Topic 1.3.3