Vars
variables
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:
- Interger
- Floating point
- Character
- Boolean
interger types
| type | bits | min value | max value | literal form |
|---|---|---|---|---|
| byte | 8 | -128 | 127 | 0 |
| short | 16 | -32768 | 32767 | 0 |
| int | 32 | -2147483648 | 2147483647 | 0 |
| long | 64 | -9223372036854775808 | 9223372036854775808 | 0L |
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
| type | bits | smallest positive value | largest positive value | literal form |
|---|---|---|---|---|
| float | 32 | $1.4 * 10^{-45}$ | $3.4 * 10^{38}$ | 0.0f |
| double | 64 | $4.9 * 10^{-324}$ | $1.7 * 10^{308}$ | 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;
storage
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.