4.5.1

Variables of Primitive Type

TYPES, VALUES, AND VARIABLES

Compatibility of the value of a variable with its type is guaranteed by the

design of the Java language. Default values are compatible ( 4.5.4) and all assign 

ments to a variable are checked for assignment compatibility ( 5.2), usually at

compile time, but, in a single case involving arrays, a run time check is made

( 10.10).

4.5.1   Variables of Primitive Type

A variable of a primitive type always holds a value of that exact primitive type.

4.5.2   Variables of Reference Type

A variable of reference type can hold either of the following:

A null reference

A reference to any object ( 4.3) whose class ( 4.5.5) is assignment compati 

ble ( 5.2) with the type of the variable

4.5.3   Kinds of Variables

There are seven kinds of variables:

1. A

class variable

 is a field declared using the keyword

static

 within a class

declaration ( 8.3.1.1), or with or without the keyword

static

 within an inter 

face declaration ( 9.3). A class variable is created when its class or interface is

loaded ( 12.2) and is initialized to a default value ( 4.5.4). The class variable

effectively ceases to exist when its class or interface is unloaded ( 12.8), after

any necessary finalization of the class or interface ( 12.6) has been completed.

2. An

instance variable

 is a field declared within a class declaration without

using the keyword

static

 ( 8.3.1.1). If a class

T

 has a field

a

 that is an

instance variable, then a new instance variable

a

 is created and initialized to a

default value ( 4.5.4) as part of each newly created object of class

T

 or of any

class that is a subclass of

T

 ( 8.1.3). The instance variable effectively ceases

to exist when the object of which it is a field is no longer referenced, after any

necessary finalization of the object ( 12.6) has been completed.

3.

Array components

 are unnamed variables that are created and initialized to

default values ( 4.5.4) whenever a new object that is an array is created

( 15.9). The array components effectively cease to exist when the array is no

longer referenced. See  10 for a description of arrays.

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