Variable Declarations




Variable names represent a place in RAM memory where we can store and retrieve a value. In the Java programming language we need to specify what type of data can be stored in the memory location.

Example:

Instance variables (available to all methods in the class).
Instance variables are defined inside the class but not
inside of a method. These variables are always available
inside of an object, as long as the object exists.
Generally we prefer that instance variables have the
accessor type of private.
  
   private int x;
   private int y = 5;
   private float z = 17.356;
   public double w = 5.6;
   public String s = "Hello World";



You can also define local (method) variables inside a method. These variables are local to the method only. They are created by the method and destroyed by the method. The variables are only in scope (available) inside the block where they are defined. You cannot use the keywords private, public, or protected on local variables. Also, you must assign a value to the variable before using the variable in an expression.

  int x = 5;   double y = 2.1;   int z;   z = 3;


Default values are for instance variables only.  If you define a local variable (inside a method), you
must assign a value to it yourself before using the variable in an expression.


Type       Bits    Default    Range (inclusive)

byte         8     0                    -128  to  127
char        16     0                       0  to  65,535   (unsigned)  
short       16     0                 -32,768  to  32,767
int         32     0          -2,147,483,648  to  2,147,483,647
float       32     0.0f       32 bit floating point number (decimals)
long        64     0L         -9,223,372,036,854,775,808  to  -9,223,372,036,854,775,807
double      64     0.0        64 bit floating point number (decimals)  
boolean      8     false      false or true


You can think of the bits as representing the size of the storage box.



Note: Variable names (as well as class names, interface names, 
      method names (i.e. identifiers)) must start with a letter 
      of the alphabet or an underscore.  We generally prefer a 
      letter.  By convention, we agree that variable names should 
      start with a lowercase letter, although the compiler
      does not enforce this.