Valid variable names:

int total;
int grade4;
int totalPer = 400;

Invalid variable names:

int 2much;

Naming styles:

int sum;
int studentCount;
int bankAccountBalance;
int level2Training;

Primative Data types:

These are the types of variables which are the foundation of all other data types. They are:

  1. Interger
  2. Floating point
  3. Character
  4. Boolean

interger types

typebitsmin valuemax valueliteral form
byte numberOfThings = 45;
short feetInAMile = 5280;
int milesToSun = 92960000;
// note the adding of L at the end of the number
// this indicates it is a long number
long milesInALightYear = 5879000000000L;

floating point types

typebitssmallest positive valuelargest positive valueliteral form
float32$1.4 * 10^{-45}$$3.4 * 10^{38}$0.0f
double64$4.9 * 10^{-324}$$1.7 * 10^{308}$0.0 or 0.0d
float kilometersInAMarathon = 42.195f;
float absoluteZeorInCelsius = -273.15f;
double atomWithInMeters = 0.0000000001d;

character data type

char regularU = 'U';
// unicode of uppercase U with an accent
char accentedU = '\u00DA';

boolean type

boolian iLoveJava = true;


Each definition of a variable gets it own allocation. When you associate a variable to an existing variable, a copy is made. There is no relation between the two. If later on, the source variable changes, the copy will remain with its original value and not be affected.