1. Statements, Comments & Simple Arithmetic4
Statements, Comments & Simple Arithmetic

2. Previously What’s Java? Some history Characteristics Components
Type of programs
Development
JVM OS
Application
Storage
Library (y)
Web Server
Storage
Browser
Library (y) OS
Servlet
Applet
applet
Interpreted language, …
JSE, JEE and JME
JDK
JVM, OS
Type: Applications, Applets, Servlets and Libraries
Development environment Eclipse

3. Overview Hello World! Reserved words & Identifiers Code Blocks Methods
Statements
Style & Comments
Simple Arithmetic & Operators

4. Finally - a Java Program!
class HiThere {
/**
* This is the entry point for an application.
astrArgs the command line arguments. */
public static void main(String[] astrArgs) {
// Starting of the main method
System.out.println("Hello World!");
} // main()
} // end class HiThere

5. Reserved words & Identifiers
class HiThere { public static void main(String[] astrArgs) { System.out.println("Hello World!"); } // main() } // end class HiThere
Reserved words or keywords are part of the language
class used to define a class
public access keyword - public, private, protected and ‘default’
static type related to belonging
void special return type
Java is case sensitive
We represent reserved words in red text.
Methods with the static keyword belong to the class when the keyword is not present then the method belong to the object (object is an instantiation of a class, holds the data with its values)

6. Reserved words & Identifiers
HiThere is an identifier
This is a name we make up to identify a component of the program (in this case a class)
Must be a single word (no blank characters)
Must start with a letter, ‘_’, ‘£’ or ‘$’
Following characters can also be numbers
Cannot contain any white space

7. Reserved words & Identifiers
The name of a classes always start in uppercase
class HiThere
The name of methods always start in lowercase
public static void main(String[] astrArgs)
The name of variables always start in lowercase
The name of static final variables (‘constants’) always in uppercase
private static final int SEC_PER_MINUTE = 60;

8. Reserved words & Identifiers
A format to build identifiers
Camel case – no word separator space, underscore
Variable names prefix with their type (lowercase)
public static void main(String[] astrArgs)
array
array of Strings
array of Strings
meaning word

9. Code Blocks
class HiThere { public static void main(String[] astrArgs) { System.out.println("Hello World!"); } // main() } // end class HiThere
Braces ( i.e. { } ) delimit an isolated block of code
All programs have several (usually many) blocks
Braces must be balanced
Braces are often nested
Control flows use also braces to delimit the block

10. Methods
class HiThere { public static void main(String[] astrArgs) { System.out.println("Hello World!"); } // main() } // end class HiThere
Methods contain blocks of functional code
Methods are named by an identifier
This is a method called main - applications execute their main method on starting (application entry point)
NB the syntax of main must be exactly as shown

11. Statements
class HiThere { public static void main(String[] astrArgs) { System.out.println("Hello World!"); } // main() } // end class HiThere
The program contains a single statement
Statements are terminated by a semi-colon
println
This statement calls a library method called System.out.println
Methods may be provided with an argument (data), which is contained in brackets

12. Statements The argument of println is a string
class HiThere { public static void main(String[] astrArgs) { System.out.println("Hello World!"); } // main() } // end class HiThere
The argument of println is a string
A string is a sequence of characters
Java strings are delimited by double quotes

13. Style
class HiThere { public static void main(String[] astrArgs) { System.out.println("Hello World!"); } // main() } // end class HiThere
indents
Line breaks and indents are ignored by the compiler, but help greatly with readability
Use meaningful names

14. Comments class HiThere { public static void main(String[] astrArgs) {
/**
* This is the entry point for an application.
astrArgs the command line arguments. */
public static void main(String[] astrArgs) {
// Starting of the main method
System.out.println("Hello World!");
} // main()
} // end class HiThere }

15. Comments Comments are ignored by the compiler
Comments may be delimited by /* */
For several lines of comment
A type of multiline comment is the documentation comments which start with /** and end with */
Comments may be delimited by // to the end of the line
Single line comment

16. Arithmetic Arithmetic is accomplished by "numeric operators“
Binary Operators
+ addition
- subtraction
* multiplication
/ division
% remainder
int iNum = 0;
iNum = 7 + 2;
iNum = 7 – 2;
iNum = 7 * 2;
iNum = 7 / 2;
iNum = 7 % 2; 9 5 14 3 1 3 1 2 3 1

17. Arithmetic 9 5 14 3 1 Arithmetic Unary Operators += addition
-= subtract
*= multiply
/= divide
%= remainder
iNum += 2;
iNum -= 2;
iNum *= 2;
iNum /= 2;
iNum %= 2;
int iNum = 7; 9 5 14 3 1

18. Arithmetic
System.out.print("The answer is "); System.out.println(2 + 2);
class Arithmetic {
/**
* Adds two to two and displays the result.
astrArgs the command line arguments, not used. */
public static void main(String[] astrArgs) {
System.out.print("The answer is ");
System.out.println(2 + 2);
} // main()
} // end class Arithmetic
The answer is 4

19. Operators Equality and Relational Operators
== equal to if (iNum == 1) {
!= not equal to if (iNum != 1) {
> greater than if (iNum > 1) {
>= greater than or equal to if (iNum >= 1) {
< less than if (iNum < 1) {
<= less than or equal if (iNum == 1) {
int iNum = 7;

20. Operators Assignment Operator Conditional Operators
&& conditional-AND
|| conditional-OR
Type Comparison Operator
instanceof compares an object to a specified type
int iNum = 7;
int iCount = 0;
if (iNum == 7 && iCounter == 0) {
true && true  true
true && false  false
false && true  false
false && false  false
true || true  true
true || false  false
false || true  true
false || false  false
? : ternary (shorthand for if-then-else statement)
<condition> ? <statement if true> : <statement if false>
if (iNum == 7 || iCounter == 0) {

21. Documentation Statement and Blocks Operators
Operators
Sun Certified Programmer for Java 5 - Study Guide

22. Lets look at HelloWorld again!
Eclipse
Lets look at HelloWorld again!