Java integer to byte

Question

I have the following code:

byte[] someArray;
int a,b;
.
.
.
a=123; (result coming from calculations, always 0>=a<256)
b=91; (result coming from calculations, always 0>=b<256)

now i want to do this

someArray[0]=a;
someArray[6]=b;

however i tried to convert in to byte to this i failed (getting all the possible error messages i think). also tried various snippets referring to integer to byte conversion.

so any idea?

update this is what i get java.lang.NumberFormatException: Invalid int: "z" when i try this byteArray[0]=Integer.valueOf(String.valueOf(bani.substring(2, 3)), 16).byteValue();

Have you tried someArray[0] = (byte) a?

chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-

2013-08-28 10:59:45 +00:00
Commented Aug 28, 2013 at 10:59 — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Aug 28, 2013 at 10:59
i updated my answer in order to invoke an exception

Philipp Sander
– Philipp Sander

2013-08-28 14:10:02 +00:00
Commented Aug 28, 2013 at 14:10 — Philipp Sander
– Philipp Sander, Commented Aug 28, 2013 at 14:10

rocketboy · Accepted Answer · 2013-08-28 10:59:44Z

2

integer -> byte conversion will result in a compilation error because it might result in precision loss. Documentation.

However, you can do an explicit cast:

someArray[0]=(byte)a;

answered Aug 28, 2013 at 10:59

rocketboy

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3 Comments

user2015552 Over a year ago

"Cannot cast from Integer to byte"... Anyway, i play in a range from 0 to 255, i can't lose anything.

rocketboy Over a year ago

Compiler keeps you from making mistakes. So it forces you to cast it explicitly.

user2015552 Over a year ago

if i do so, the application compiles, but it crashes when it gets to cast.

Philipp Sander · Accepted Answer · 2013-08-28 14:09:19Z

2

Be aware that Byte is not 0 to 255! It is -128 to +127

if you are aware of this, simply cast the values

someArray[0] = (byte) a;
someArray[6] = (byte) b;

But srround it with a check because java will cast you everything:

if(value <= Byte.MAX_VALUE && value >= Byte.MIN_VALUE) {
    //do the cast
}
else {
    //error handling
}

for example:

int i = 1300;
byte b = (byte) i;
//b will be 20 here

UPDATE:

If you want to envoke a NumberFormatException you can parse the value like this:

Byte.valueOf(Integer.toString(value));

Remember that byte is from -128 to 127!

edited Aug 28, 2013 at 14:09

answered Aug 28, 2013 at 10:59

Philipp Sander

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Comments

GerritCap · Accepted Answer · 2013-08-28 11:05:35Z

0

In Java integral primitive types (byte, short, int, long) are always signed.

Hence a byte is always -128...127

You can convert an int to a byte by using casting

int i = 120;

byte b = (byte) i;

if you assign 200 to i instead of 120, then b becomes -56, assigning b back to i then i will remain -56 and not turn to 200 again.

This is because the binary representation of 200 is 11001000, and put these bits into a byte then it is interpreted as -56, putting this into an int again makes it into 1111111111111111111111001000

answered Aug 28, 2013 at 11:05

GerritCap

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Comments

Eng.Fouad · Accepted Answer · 2013-08-28 11:10:04Z

0

First of all, ~~there is no unsigned data type in Java. All of them are signed~~ byte is signed data type and can hold values in the range -128 <= b => 127. Secondly, you need to subtract 128 from the integer value and then cast it to byte, just to get a value that byte can hold:

someArray[0] = (byte) (a - 128);
someArray[6] = (byte) (b - 128);

edited Aug 28, 2013 at 11:10

answered Aug 28, 2013 at 10:59

Eng.Fouad

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3 Comments

dnet Over a year ago

-1 By doing this, if a = 1, someArray[0] has the value -127, see pastebin.com/sMDMUycm

Simon Nickerson Over a year ago

It's also not true that there's no unsigned data type in Java. char is unsigned.

Eng.Fouad Over a year ago

@dnet You didn't understand what I am saying. byte cannot hold the values > 127 since it is signed. What I suggested is to subtract 128 from the integer value just for getting a value that byte can hold.

Kris · Accepted Answer · 2013-08-28 11:13:16Z

0

I am not sure about how far the application you develop this for concerns memory usage :-). We have an API Bytes.toBytes() in HBase API. You can use this API to get a byte representation of a lot of types. May be you can use the reverse of it like Bytes.toInt() for converting back. As far i seen, no issue of precision loss or value change is seen.

You can download the lib from here Hbase Lib .. Add the hbase-0.94.jar from the lib to your project.

answered Aug 28, 2013 at 11:13

Kris

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Comments

le-doude · Accepted Answer · 2013-08-28 13:34:51Z

0

To guarantee no error for values above Byte.MAX_VALUE and below Byte.MIN_VALUE you could use bitwize operations to impose a max value:

public static byte toByte(int i){
    return (byte) (i & 0x000000ff);
}

This will ignore all bites above the first 8. Thus giving you a valid byte from any int (with the loss of the 24 highest order bits).

If you use this operation a lot this byte far faster than comparison and cast.

answered Aug 28, 2013 at 13:34

le-doude

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