Since Variables stand for items that the program is
manipulating
or playing with, such as:
whole numbers (small
normal large)
fractional numbers (small
large)
single characters
groups of characters as a unit
true / false conditions
it is only logical to assume that JAVA gives the
programmer the
capability to declare and use Variables that can hold each of the
above data types. Remember that values ( or data ) being
put into
Variables is the heart or basis of programming.
Variables MUST be declared before they can be used in a program.
Common Variable types are as follows:
short
... small integers
int
... normal integers
long
... big integers
float
... small fractional numbers
double
... big fractional numbers
char
... single character values e.g.,
M or F
string
... groups of characters viewed as a unit
Boolean
... logical TRUE or FALSE values
In object oriented and more sophisticated programs today, the
programmer can declare his or her own data type ( later )
Specifics concerning Java Data TYpes
NUMERIC (all numbers are signed)
short integer (16 bit number) --> i.e. 32,768
int integer (32 bit number) --> i.e. 2 billion or 2 x 109
long integer (64 bit number) --> i.e. 9 x 1018
float real (32 bit decimal) --> i.e. 1.4 x 10-45 to 3.4 x 1038
double real (64 bit decimal) --> i.e. 4.9 x 10-324 to 1.7 x 10308
char a unicode (2-byte) char
the String class handles multi-character strings (strings are unicode,
as well). Strings are said to be immutable: updates to a String cause
the new string to be created in memory (and pointed to by the String
class). However the old string is not actually "updated",
rather, its reference is lost (and it becomes available for garbage
collection).
BOOLEAN
boolean (with values true, false)
DATE
the Date class measures the milliseconds since Jan 1, 1970 and provides
supporting functions to interpret and manipulate date/times
ARRAYS
arrays hold multiple instances of a data type or object
