casting int to byte

[Rob Shepherd]

when applying (byte)bit masks to bytes, do i always have to cast my mask in to a byte.

[just realizing i've even had to do it in previous sentence ]

javac output is thus.

....
operator && cannot be applied to byte,int
length += ((packet[13] && 0x0f) << 4);
....

does the compiler assume 0x0f is an int as it would if a long or float value were not
suffixed L or F respectively.

I gather i will not be able to add a 'b' or 'B' to the end of my value (being Hex digits).

I'm getting annoyed with casting all the time!!!

For freq used masks i make

static final byte MASK = 0x??;

which the compiler obviously has no problems with....

I'd rather not make 255 final byte masks though!!!

regards

Rob

 

[Kristoffel]

when applying (byte)bit masks to bytes, do i always have to cast my mask
in to a byte.

[just realizing i've even had to do it in previous sentence ]

javac output is thus.

...
operator && cannot be applied to byte,int
length += ((packet[13] && 0x0f) << 4);

(packet[13] && 0x0f) results in a boolean !

I assume that it should be
length += ((packet[13] & 0X0F) << 4);

with one '&'

 

[Rob Shepherd]

when applying (byte)bit masks to bytes, do i always have to cast my
mask in to a byte.

[just realizing i've even had to do it in previous sentence ]

javac output is thus.

...
operator && cannot be applied to byte,int
length += ((packet[13] && 0x0f) << 4);

(packet[13] && 0x0f) results in a boolean !

I assume that it should be
length += ((packet[13] & 0X0F) << 4);

with one '&'

...

does the compiler assume 0x0f is an int as it would if a long or float
value were not suffixed L or F respectively.

I gather i will not be able to add a 'b' or 'B' to the end of my value
(being Hex digits).

I'm getting annoyed with casting all the time!!!

For freq used masks i make

static final byte MASK = 0x??;

which the compiler obviously has no problems with....

I'd rather not make 255 final byte masks though!!!

regards

Rob

Yeah... my bad!! i'm having a confusing afternoon!! too much bit-banging
please ignore!!

thanks Kristoffel.


Ro

 

[Roedy Green]

when applying (byte)bit masks to bytes, do i always have to cast my mask in to a byte.

[just realizing i've even had to do it in previous sentence ]

If you cast them to bytes, you are just truncating the high order
bits. The operators such as & + | all work on ints, and any bytes will
be automatically widened back to ints. Unfortunately bytes are signed,
so automatic widening will just put high order bits back on again.

Use & 0xff instead when you want unsigned bytes.


See http://mindprod.com/jgloss/unsigned.html

 

[Roedy Green]

(packet[13] && 0x0f) results in a boolean !

No, it result in an syntax error. && will only operate on booleans
in Java.

You want &, the bitwise operator.

 

[Liz]

when applying (byte)bit masks to bytes, do i always have to cast my mask in to a byte.

[just realizing i've even had to do it in previous sentence ]

If you cast them to bytes, you are just truncating the high order

You can't truncate the high order bits
trun·cate
trun·cate (trùng¹kât´) verb, transitive
trun·cat·ed, trun·cat·ing, trun·cates
1. To shorten................
2. To shorten (a number) by dropping one or more digits after the
decimal point.
3. To replace................

 

[Roedy Green]

You can't truncate the high order bits
trun·cate
1. To shorten................

You are shortening the "payload". I suppose I could have said
zero-out or mask-off the high order bits.