CONVERSIONS AND PROMOTIONS

Unary Numeric Promotion

5.6.1

5.6.1   Unary Numeric Promotion

Some operators apply

unary numeric promotion

 to a single operand, which must

produce a value of a numeric type:

If the operand is of compile time type

byte

,

short

, or

char

, unary numeric

promotion promotes it to a value of type

int

 by a widening conversion

( 5.1.2).

Otherwise, a unary numeric operand remains as is and is not converted.

Unary numeric promotion is performed on expressions in the following situations:

The dimension expression in array creations ( 15.9)

The index expression in array access expressions ( 15.12)

Operands of the unary operators plus

+

 ( 15.14.3) and minus

 ( 15.14.4)

The operand of the bitwise complement operator

~

 ( 15.14.5)

Each operand, separately, of the shift operators

>>

,

>>>

, and

<<

 ( 15.18), so

that a

long

 shift distance (right operand) does not promote the value being

shifted (left operand) to

long

Here is a test program that includes examples of unary numeric promotion:

class Test {

public static void main(String[] args) {

byte b = 2;

int a[] = new int[b]; //

dimension expression promotion

char c =  \u0001 ;

a[c] = 1;

//

index expression promotion

a[0] =  c;

//

unary

 promotion

System.out.println("a: " + a[0] + "," + a[1]);

b =  1;

int i = ~b;

//

bitwise complement promotion

System.out.println("~0x" + Integer.toHexString(b)

+ "==0x" + Integer.toHexString(i));

i = b << 4L;

//

shift promotion (left operand)

System.out.println("0x" + Integer.toHexString(b)

 + "<<4L==0x" + Integer.toHexString(i));

}

}

This test program produces the output:

a:  1,1

~0xffffffff==0x0

0xffffffff<<4L==0xfffffff0

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