CODEWITHSUNDEEP
java
user2015552
user2015552

Reputation: 125

Java integer to byte

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();

Upvotes: 0

Views: 638

Answers (6)

Philipp Sander
Philipp Sander

Reputation: 10239

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!

Upvotes: 2

le-doude
le-doude

Reputation: 3367

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.

Upvotes: 0

Kris
Kris

Reputation: 8868

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.

Upvotes: 0

Eng.Fouad
Eng.Fouad

Reputation: 117589

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);

Upvotes: 0

GerritCap
GerritCap

Reputation: 1616

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

Upvotes: 0

rocketboy
rocketboy

Reputation: 9741

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;

Upvotes: 2

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