SalesForce.Com (sfdc) - Primitive Data Type

Data types such as integer, Double, Long, Date, Date Time, String, ID, Boolean, etcs.. are primitive data types in sfdc that are can passed by value not by reference.

Boolean; vaiables that set as true or false or null.
Date; value that indicate a particular day,
          created by system static method,
syntax, Date dt=Date.newInstance(2014,01,06) will produce 2014-01-06 00:00:00

Time and Date Time; we can construct date and time values as;

Time t=Time.newInstance(11,30,3,3) output result 11:30:03.003Z
Datetime dt=Datetime.now() output result 2014-01-06 11:30:03
Date dt=Date.today() out result 2014-01-06 00:00:00
Time t=DateTime.now().time() output result 11:30:03.003Z

Integer; 32 bit number that doesnt include decimal points
             start from -2,147,483,648 to 2,147,483,647


Long; 64 bit number that doesnt include decimal points
          start from -2^63 to 2^63-1


Double; 64 bit number with decimal points
          start from -2^63 to 2^63-1

Decimal; 32 bit number with decimal points
       
Null; declared vaiables that not initialized to any value.
         null means absent of a value.

String; are set of characters set in a quotes (' or "")