Java Constants

• Examples of integer constants:
  354, -37, 0, 246543 (no commas).

• Examples of floating point constants:
  4.642, -0.034, 5.98e24 (mass of earth), 9.11e-31 (mass of electron)

• Examples of character constants:
  'A', 'y', '8', '*', ' ' (space), '\n' (new line).

  A character can be stored in memory using its ASCII Code. ASCII means American System of Computer Information Interchange. Here is a Table of ASCII Codes.

  Actually, Java uses the Unicode system for storing characters which includes the ASCII codes as a subset. For more information on Unicode, see this link: http://www.unicode.org.

  Here are the Java escape sequences:

  Escape Sequence	Meaning
  \b	backspace
  \f	form feed
  \n	line feed
  \r	carriage return
  \t	tab
  \"	double quote
  \'	single quote
  \\	backslash

• Boolean constants:
  true, false

Java Variables

• Name   The string of letters in a program used to designate a variable.
  
  A name should start with a letter and consist of letters and/or digits.
  Variables in names are case sensitive (capitalization matters).
  The naming convention in Java is to start a variable name with a lower case letter.
  New words within a name with a name start with a capital letter
  (example: numberOfCustomers).

• Value   The binary data contained in memory. The value is interpreted according to the variable's datatype.

• Address   The location in memory where the value is stored.

• Size   The number of bytes that the variable occupies in memory.

• Datatype   The interpretation of the value. Some important datatypes are listed in the following table.

• Range   The minimum and maximum values of the variable. The range of a variable depends on its size. In general, the bigger the size in bytes, the bigger the range.

Variable initialization in declaration:
int timeInSeconds = 245;
char a = 'K', b = '$';
boolean flag = true;
double maxVal = 35.875;

Java Primitive Datatypes

Datatype	Meaning	Size in Bytes	Min Value	Max Value	Sig. Digits
int	Integer	4	-2 billion	2 billion
double	Floating Point	8	-1.8x10308	1.8x10308	15
char	Character	2	Any Unicode character
boolean	Logical	1	false	true

String Objects