1. IT151: Introduction to Programming
Introduction to Java Applications

2. // Text-printing program
// Created by: Siua Fonua
// Date: 14 Feb 2006
public class Welcome {
// main method begins execution of Java Applications
public static void main (String args[ ])
System.out.println(“Welcome to IT151”);
System.out.println(“Enjoy programming with Java”);
} // end main method
} // end class Welcome

3. Line 1 – Line 3 Comments Begins with //
Comments are used to improve the program’s readability
Java compiler ignores all comments
To ways of indicating a comment
// end-of-line comment
/* … */ multiple-line comments

4. Line 4, 12 White space Includes Makes the program easier to read
Blank lines
Space characters
Tab characters
Makes the program easier to read
Ignored by the compiler

5. Line 5 Class declaration
Every program in Java consists of at least one class
The keyword class is used to declare a class, followed by the name of the class
The name of the class is called it’s identifier
NOTE:
YOU MUST DECLARE EVERYTHING IN JAVA

6. Reserved Words Also known as keywords
These words are reserved for use by Java
Examples include:
class
Public, and more to come
Don’t use any of the Java keywords for your own use. IT WILL CONFUSE THE COMPILER

7. Class Names Rules for naming your class Convention Contains only
Letters
Digits
Underscore ( _ )
Dollar sign ( $ )
Does not contain spaces
Does not begin with a digit
Convention
All class names begin with a capital letter
Capitalise the first letter of each word they include

8. Java is case-sensitive
That is:
Uppercase and lowercase letters are distinct
Examples:
TIHE is different from Tihe or tihe
Not using the correct letters for an identifier causes a compilation error

9. Public classes Every class you declared public:
Must be saved in its own file
Class name must be the same as the filename
Must be ended with the .java extension
Failing to follow these rules, result in errors
Sometimes your class will not be compiled by the compiler

10. Line 6, 14 Left brace, { Right brace, }
Begins the body of the class
Right brace, }
Ends the body of the class
It is a syntax error if braces do not occur in matching pairs

11. Line 8 The starting point of every Java applications
Your program must have this line, exactly as it is shown here!
Otherwise, your program will not be compiled by the compiler

12. Methods A block of code in the program that performs a specific task
Methods are able to perform a task and returns information when they complete execution
Some methods will not return any information when they complete execution
All methods will have
Return type
Method name
List of parameters (inside a pair of parentheses)

13. void methods
When the keyword void appears in front of the method name, it indicates that this method will NOT return anything when it completes execution
We’ll discuss later, the methods that will return information after execution

14. Line 9, 13 Left brace, { Right brace, }
Begins the body of the method
Right brace, }
The end of the method’s body
Whatever is between these braces, will be the actions to be performed by the method

15. Line 10 Instructs the computer to perform an action That is:-
To print a string of characters contained between the double quotation marks
White-space characters in strings are not ignored by the compiler

16. Standard output System.out is called the standard output object
Allows Java to display sets of characters in the window from which Java executes

17. System.out.println
This method displays a line of text in the command window
Needs an argument, which is a string of characters
Outputs its argument to the command window
After completion, it positions the output cursor in the next line

18. Line 11
What does this line do?

19. Statement The entire line 10, is called a statement
Each statement MUST end with a semicolon
A method is typically composed by one or more statements that performs the method’s task
NOTE: omitting the semicolon at the end of a statement, is a syntax errorh

20. // Text-printing program
// Created by: Siua Fonua
// Date: 14 Feb 2006
public class Welcome {
// main method begins execution of Java Applications
public static void main (String args[ ])
System.out.print(“Welcome to IT151”);
System.out.println(“Enjoy programming with Java”);
} // end main method
} // end class Welcome

21. // Text-printing program
// Created by: Siua Fonua
// Date: 14 Feb 2006
public class Welcome {
// main method begins execution of Java Applications
public static void main (String args[ ])
System.out.println(“Welcome\n to\n IT151”);
System.out.println(“Enjoy programming with Java”);
} // end main method
} // end class Welcome

22. Escape characters
The backslash (\) is called an escape character in Java \n \t \r \\ \”