04 - Variables and Data Types

1>> id speedLimit = 80

2>> int speedLimit > 80;

3>> speedLimit = 80

4>> int speedLimit = 80;

5>> dim speedLimit = 80;

6>> var speedLimit = 80;

int maxSpeed =30;

0000000000000000

Read and remember this definition: variable ? a named location in main memory 
which uses a particular data type to hold a value.Also, note that a variable
cannot be used in a program unless it has been declared. 

class Example
{
  public static void main ( String[] args )
  {
    long payAmount = 123; 

    System.out.println("The variable contains: " + payAmount );
  }
}

There are types of data that are so fundamental that ways to 
represent them are built into Java

The list below shows ___________ Data Types
=======================

byte
short
int
long
float
double
char
boolean

Similarly, "Int" is not valid, but "int" is.

int - primitive
String - primitive
double - primitive
Scanner - class
short - primitive

125  
-32  
16  
0  
-123987

The ____ type represents a character using 16 bits. 
In many programming languages, only 8 bits are used for this purpose. 
Java uses 16 bits so that a very large number of characters can be 
represented, nearly all of the characters in all of the World's languages.
 The method used is called Unicode. 

A character literal is a single character with an apostrophe on each side: 
'm'       'y'         'A'
A control character is represented with a special sequence of characters: 
'\n'       '\t'

"testandtrack"

Additional important note:
==========================
There are two types of variables in Java, 
>>primitive and 
>>reference type.

All the basic types e.g. int, boolean, char, short, float, long and 
double are known as primitive types. JVM treats them differently 
than reference types, which is used to point objects e.g. 
String, Thread, File and others.

class Example
{
  public static void main ( String[] args )
  {
    long pAmount = 777;    //the declaration of the variable

    System.out.println("The variable contains: " + pAmount );
  }
}

Use only the characters 'a' through 'z', 'A' through 'Z', 
Use only '0' through '9', character '_', and character '$'.
An identifier can not contain the space character.
Do not start with a digit.
An identifier can be any length.
Upper and lower case count as different characters. 
SUM  and  Sum  are different identifiers.
An identifier can not be a reserved word.
An identifier must not already be in use in this part of the program.

int myPay, yourPay; // OK
long good-by ;  // bad identifier: "-" not allowed
short shrift = 0;  // OK
double bubble = 0, toil= 9, trouble = 8 // missing ";" at end.
byte the bullet ;    // bad identifier: can't contain a space
int  double;    // bad identifier: double is a reserved word
char thisMustBeTooLong  ;   // OK in syntax, but a poor choice 
                            // for a variable name
int  8ball;    // bad identifier: can't start with a digit
float a=12.3; b=67.5; c= -45.44; 

class CharExample {
    public static void main(String[] args) {
    	
    	char letter = '\u0051';
    	System.out.println(letter);
    }
}

myString = "Thanks, www.testandtrack.io";

There are 4 types of variables in Java:
=======================================
1-Instance Variables (Non-Static Fields)
2-Class Variables (Static Fields)
3-Local Variables
4-_______________