Reputation: 2333

Java integer to byte array

I got an integer: 1695609641

when I use method:

String hex = Integer.toHexString(1695609641);
system.out.println(hex);

gives:

6510f329

but I want a byte array:

byte[] bytearray = new byte[] { (byte) 0x65, (byte)0x10, (byte)0xf3, (byte)0x29};

How can I make this?

Upvotes: 233

Answers (15)

user9532210

Reputation: 19

I came here looking for the best way to do this, but then decided to go with:

String.valueOf(<your-int>).getBytes()

It was simpler for my purposes (writing an int to a file). Not to mention that when encoding you can use less than 4 bytes for small values (ascii) vs. encoding a 32-bit int.

Upvotes: 0

light

Reputation: 180

Here are two function to do the mirrored thing:

    byte[] intToBytes(int i) {
        return new byte[]{
                (byte) (i >>> 24),
                (byte) (i >>> 16),
                (byte) (i >>> 8),
                (byte) i
        };
    }

    int bytesToInt(byte[] b) {
        //Cuz int encode by complement-on-two
        //For a negative, signed left shift operation will Fill the upper part of the binary with 1.
        //That‘s a question for us to combine the meaningful part.

        //Here, we execute a AND 0xFF operation, to implicitly convert a byte to int, and fill  the upper part of the binary with 0
        //So ,we got a positive number now.
        //The next step just execute OR operation to combine the four part as an integer.
        return (b[0]) << 24 |
                (b[1] & 0xFF) << 16 |
                (b[2] & 0xFF) << 8 |
                (b[3] & 0xFF);
    }

Upvotes: 0

Yury Finchenko

Reputation: 1065

byte[] IntToByteArray( int data ) {    
    byte[] result = new byte[4];
    result[0] = (byte) ((data & 0xFF000000) >> 24);
    result[1] = (byte) ((data & 0x00FF0000) >> 16);
    result[2] = (byte) ((data & 0x0000FF00) >> 8);
    result[3] = (byte) ((data & 0x000000FF) >> 0);
    return result;        
}

Upvotes: 34

Neeraj

Reputation: 2558

If you're using apache-commons

public static byte[] toByteArray(int value) {
    byte result[] = new byte[4];
    return Conversion.intToByteArray(value, 0, result, 0, 4);
}

Upvotes: 5

jytou

Reputation: 550

Because generally you would want to convert this array back to an int at a later point, here are the methods to convert an array of ints into an array of bytes and vice-versa:

public static byte[] convertToByteArray(final int[] pIntArray)
{
    final byte[] array = new byte[pIntArray.length * 4];
    for (int j = 0; j < pIntArray.length; j++)
    {
        final int c = pIntArray[j];
        array[j * 4] = (byte)((c & 0xFF000000) >> 24);
        array[j * 4 + 1] = (byte)((c & 0xFF0000) >> 16);
        array[j * 4 + 2] = (byte)((c & 0xFF00) >> 8);
        array[j * 4 + 3] = (byte)(c & 0xFF);
    }
    return array;
}

public static int[] convertToIntArray(final byte[] pByteArray)
{
    final int[] array = new int[pByteArray.length / 4];
    for (int i = 0; i < array.length; i++)
        array[i] = (((int)(pByteArray[i * 4]) << 24) & 0xFF000000) |
                (((int)(pByteArray[i * 4 + 1]) << 16) & 0xFF0000) |
                (((int)(pByteArray[i * 4 + 2]) << 8) & 0xFF00) |
                ((int)(pByteArray[i * 4 + 3]) & 0xFF);
    return array;
}

Note that because of sign propagation and such, the "& 0xFF..." are needed when converting back to the int.

Upvotes: 4

Aleksandr Dubinsky

Reputation: 23505

Using Guava:

byte[] bytearray = Ints.toByteArray(1695609641);

Upvotes: 29

superbob

Reputation: 1638

My try :

public static byte[] toBytes(final int intVal, final int... intArray) {
    if (intArray == null || (intArray.length == 0)) {
        return ByteBuffer.allocate(4).putInt(intVal).array();
    } else {
        final ByteBuffer bb = ByteBuffer.allocate(4 + (intArray.length * 4)).putInt(intVal);
        for (final int val : intArray) {
            bb.putInt(val);
        }
        return bb.array();
    }
}

With it you can do this :

byte[] fourBytes = toBytes(0x01020304);
byte[] eightBytes = toBytes(0x01020304, 0x05060708);

Full class is here : https://gist.github.com/superbob/6548493, it supports initialization from shorts or long

byte[] eightBytesAgain = toBytes(0x0102030405060708L);

Upvotes: 1

lyon819

Reputation: 89

public static byte[] intToBytes(int x) throws IOException {
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    DataOutputStream out = new DataOutputStream(bos);
    out.writeInt(x);
    out.close();
    byte[] int_bytes = bos.toByteArray();
    bos.close();
    return int_bytes;
}

Upvotes: 7

HaoQi Li

Reputation: 12350

The chunks below work at least for sending an int over UDP.

int to byte array:

public byte[] intToBytes(int my_int) throws IOException {
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    ObjectOutput out = new ObjectOutputStream(bos);
    out.writeInt(my_int);
    out.close();
    byte[] int_bytes = bos.toByteArray();
    bos.close();
    return int_bytes;
}

byte array to int:

public int bytesToInt(byte[] int_bytes) throws IOException {
    ByteArrayInputStream bis = new ByteArrayInputStream(int_bytes);
    ObjectInputStream ois = new ObjectInputStream(bis);
    int my_int = ois.readInt();
    ois.close();
    return my_int;
}

Upvotes: 2

mlohbihler

Reputation: 777

The class org.apache.hadoop.hbase.util.Bytes has a bunch of handy byte[] conversion methods, but you might not want to add the whole HBase jar to your project just for this purpose. It's surprising that not only are such method missing AFAIK from the JDK, but also from obvious libs like commons io.

Upvotes: 1

vmpn

Reputation: 701

BigInteger.valueOf(1695609641).toByteArray()

Upvotes: 58

dfa

Reputation: 116304

using Java NIO's ByteBuffer is very simple:

byte[] bytes = ByteBuffer.allocate(4).putInt(1695609641).array();

for (byte b : bytes) {
   System.out.format("0x%x ", b);
}

output:

0x65 0x10 0xf3 0x29

Upvotes: 354

Carl Smotricz

Reputation: 67750

byte[] conv = new byte[4];
conv[3] = (byte) input & 0xff;
input >>= 8;
conv[2] = (byte) input & 0xff;
input >>= 8;
conv[1] = (byte) input & 0xff;
input >>= 8;
conv[0] = (byte) input;

Upvotes: 7

Grzegorz Oledzki

Reputation: 24251

How about:

public static final byte[] intToByteArray(int value) {
    return new byte[] {
            (byte)(value >>> 24),
            (byte)(value >>> 16),
            (byte)(value >>> 8),
            (byte)value};
}

The idea is not mine. I've taken it from some post on dzone.com.

Upvotes: 189

Brian Agnew

Reputation: 272217

integer & 0xFF

for the first byte

(integer >> 8) & 0xFF

for the second and loop etc., writing into a preallocated byte array. A bit messy, unfortunately.

Upvotes: 2

Java integer to byte array

Answers (15)

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