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 	void main() {

	}

This is the core inside which we start to program. Every program must go inside a void main() function which is followed by curly brackets { }

Statements are :

Single executable actions.
They usually end with a semi-colon ( ; )

Functions are calls to action , they do something.
eg printLine("this"); // prints out "this"
main() // makes the whole program execute
readInt() // reads in an integer typed in by a user

Variables

Variables are divided into different sections. They stand for a value and can be changed by the program. They must be declared what type they are at the start of a program. Notice after each line or statement is finished with a semi-colon ( ; ) .

Rules for variables:

The first character must be a letter, not a number.
Remaining positions can be filled with numbers or letters and "_"
Don't have any spaces
Variables are case-sensitive. They must be written the same way every time. e.g. Price is not the same as price
It is usual for variables to start with a lower-case letter and any subsequent words be capitalized. e.g. costPrice, sellingPrice, myAge , theNumber.
Make variables names understandable. Use real words that describe what it does. e.g. rectangleWidth, boxLength, carSpeed, cricketScore .

These variable names are illegal : 2formula, 24_Cost, egg Cost .

Exercises
1. which of these variable names are legal ?
a. result b. Product1 c. a d. textbox e. text1 f. field_2 g. stackDepth h. ball Speed

Declaration
All variables must be declared. That is, they must tell the compiler what type of data they are (datatype). Datatypes can be a number such as int or double. Or text such as a String. Or a true/false datatype called a boolean.
These are declarations:

	int myAge;
	double price;
	String myName;
	boolean likesJava;

Initialization
Initialization must be done after the declaration. Its purpose is to give a value to the variable. If given no value, Java assumes that the value is 0, or false for a boolean.
Here are examples of initialization:

	myAge     = 14;
	price     = 12.95;
	myName    = "Fred Durst";
	likesJava = false;

Variables can be declared and initialized in the one line:

	int myAge         = 14;
	double price      = 12.95;
	String myName     = "Fred Durst";
	boolean likesJava = false;

Declaration and initialization should be done at the top of the program before the variables are used.

Number Variables
int - integer or whole numbers such as 3, 9, 32, 456

	int age = 9;
	int year = 2003;

double - numbers with a decimal point in them such as 1.00 , 34.54, 234.07

	double price = 12.45;
	double pi = 3.412;

Text Variables
String
- a sequence of characters or letters such as "a string of text", "Steve Happ", "GameBoy 3.34".
- Strings are always enclosed inside Quotation marks - " ".


	String myName = "Steve Happ";
	String gameType = "Shoot 'em up";

Truth Variables
boolean - is either "true" or "false"

	boolean isLearningJava = true;
	boolean likesIceCreams = false;

(Just joking ! )

Color Variables
Color

	Color shirtColor = red;
	Color myCatColor = yellow;

Comments

Comments start a line with "//" . They are not executed. They are inserted by the programmer to explain what she is doing. And when coming back later, you or another programmer can quickly follow what has been done. Now lets write a program that uses these ideas.

	void main() {
		// declaration and initialization of variables
		int sum = 4 + 3;
		double price =  12.34;
		String book = "Learning Java";
		String name = "Steve Happ";

		// do the programming work
		printLine("Attention Computer Book Shop");
		printLine("I want to buy " + sum + book +
		" at the price of $" + price);
		printLine("Yours Sincerely");
		printLine(name);
	}

Type in the above code (in red) into the code window and press the "Run" button. What did you get ?

Notes on program above

See that I have used ( // ) in some lines at the start. These are comments and are not read when the code runs. They are meant to be notes to oneself to help remember what you are doing throughout the code and for others to be able to follow what you have written. They also break up the program into structural chunks .
```
	// this is a line of comment
	// and will not be processed
	// it is used for reminders to oneself
	// and for structural purposes
```
printLine is a command which does what ? Good guess ! It prints a line out . The usage is as follows:
```
	printLine("Whatever is between the quotes will be printed") ;
```
When you want to print a section of text and follow it with a variable you use the "+" character. As in :
```
	printLine("My name is " + name);
```
This will print out :
My name is Steve Happ
Sorry, I left out a period. So I must add a "." with a "+" after name. Here is what it will look like:
```
	printLine("My name is " + name + ".") ;
```
Try this :
```
	printLine("My name is " + name + ", and my age is " + age) ;
```
Whoops! I forgot the period again. You fix up my mistake.

Key words

These words are reserved--you cannot use any of these words as names of variables in your programs.

abstract	double	int	strictfp
boolean	else	interface	super
break	extends	long	switch
byte	final	native	synchronized
case	finally	new	this
catch	float	package	throw
char	for	private	throws
class	goto	protected	transient
const	if	public	try
continue	implements	return	void
default	import	short	volatile
do	instanceof	static	while