4.5.4

Initial Values of Variables

TYPES, VALUES, AND VARIABLES

The following example contains several different kinds of variables:

class Point {

static int numPoints;

// numPoints

 is a class variable

int x, y;

// x

 and

y

 are instance variables

int[] w = new int[10];

// w[0]

 is an array component

int setX(int x) {

// x

 is a method parameter

int oldx = this.x;

// oldx

 is a local variable

this.x = x;

return oldx;

}

}

4.5.4   Initial Values of Variables

Every variable in a Java program must have a value before its value is used:

Each class variable, instance variable, or array component is initialized with a

default value

 when it is created ( 15.8,  15.9,  20.3.6):

N

For type

byte

, the default value is zero, that is, the value of

(byte)0

.

N

For type

short

, the default value is zero, that is, the value of

(short)0

.

N

For type

int

, the default value is zero, that is,

0

.

N

For type

long

, the default value is zero, that is,

0L

.

N

For type

float

, the default value is positive zero, that is,

0.0f

.

N

For type

double

, the default value is positive zero, that is,

0.0d

.

N

For type

char

, the default value is the null character, that is,

 \u0000 

.

N

For type

boolean

, the default value is

false

.

N

For all reference types ( 4.3), the default value is

null

.

Each method parameter ( 8.4.1) is initialized to the corresponding argument

value provided by the invoker of the method ( 15.11).

Each constructor parameter ( 8.6.1) is initialized to the corresponding argu 

ment value provided by a class instance creation expression ( 15.8) or explicit

constructor invocation ( 8.6.5).

An exception handler parameter ( 14.18) is initialized to the thrown object

representing the exception ( 11.3,  14.16).

A local variable ( 14.3,  14.12) must be explicitly given a value before it is

used, by either initialization ( 14.3) or assignment ( 15.25), in a way that can

be verified by the compiler using the rules for definite assignment ( 16).

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