CONVERSIONS AND PROMOTIONS

Narrowing Primitive Conversions

5.1.3

The example:

class Test {

public static void main(String[] args) {

float fmin = Float.NEGATIVE_INFINITY;

float fmax = Float.POSITIVE_INFINITY;

System.out.println("long: " + (long)fmin +

".." + (long)fmax);

System.out.println("int: " + (int)fmin +

".." + (int)fmax);

System.out.println("short: " + (short)fmin +

".." + (short)fmax);

System.out.println("char: " + (int)(char)fmin +

".." + (int)(char)fmax);

System.out.println("byte: " + (byte)fmin +

".." + (byte)fmax);

}

}

produces the output:

long:  9223372036854775808..9223372036854775807

int:  2147483648..2147483647

short: 0.. 1

char: 0..65535

byte: 0.. 1

The results for

char

,

int

, and

long

 are unsurprising, producing the minimum

and maximum representable values of the type.

The results for

byte

 and

short

 lose information about the sign and magni 

tude of the numeric values and also lose precision. The results can be understood

by examining the low order bits of the minimum and maximum

int.

 The mini 

mum

int

 is, in hexadecimal,

0x80000000

, and the maximum

int

 is

0x7fffffff

.

This explains the

short

 results, which are the low 16 bits of these values, namely,

0x0000

 and

0xffff

; it explains the

char

 results, which also are the low 16 bits of

these values, namely,

 \u0000 

 and

 \uffff 

; and it explains the

byte

 results,

which are the low 8 bits of these values, namely,

0x00

 and

0xff

.

A narrowing conversion from

double

 to

float

 behaves in accordance with

IEEE 754. The result is correctly rounded using IEEE 754 round to nearest mode.

A value too small to be represented as a

float

 is converted to positive or negative

zero; a value too large to be represented as a

float

 is converted to a (positive or

negative) infinity. A

double

 NaN is always converted to a

float

 NaN.

Despite the fact that overflow, underflow, or other loss of information may

occur, narrowing conversions among primitive types never result in a run time

exception ( 11).

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