up vote 38 down vote favorite
12

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?? :D

thnx!

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possible duplicate of Convert integer into byte array (Java) – finnw Jul 27 '10 at 14:14

8 Answers

up vote 65 down vote accepted

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
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Or use the format "0x%02X" if you always want two hexadecimal characters as well as uppercase hexadecimals, e.g. System.out.format("0x%02X", (byte) 10) displays 0x0A. – owlstead Jan 8 '12 at 13:01
   
ByteBuffer.allocate() doesn't seem to exist but allocateDirect() does. I'm going with that. – conor Mar 6 '12 at 15:49
@conor Javadoc says that allocateDirect() does have a cost and should be used when a buffer is kept for a while. Although the answer works it seems to be a bit of overkill for the use case at hand. – Luis Soeiro Aug 22 '12 at 17:30
up vote 31 down vote

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.

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2  
-1 Not a good idea to hand-code things like this; that's what properly-tested and reviewed JDK libraries are for. – Kevin Bourrillion Feb 2 '10 at 15:33
13  
I see your point, but for this particular task 'my' code is more declarative and clear than some 'magic' ByteBuffer, which one has to check to see what it does. – Grzegorz Oledzki Feb 2 '10 at 20:50
9  
@Kevin - that's very harsh - there are plenty of cases where this kind of code is appropriate, e.g. in image processing. The JDK libraries are great in general, but they don't cover and/or aren't optimised for all use cases. – mikera Apr 26 '11 at 14:50
6  
agreed; the overhead and complexity of ByteBuffer may not be appropriate compared to some simple and well known byte operations. – swdunlop May 3 '11 at 2:27
1  
Another point I'd add is that you've used the unsigned right shift operator >>> rather than the right shift operator >> (docs.oracle.com/javase/tutorial/java/nutsandbolts/op3.html) so behavior may not be as desired/as expected with signed vs unsigned numbers – RobV May 7 '12 at 11:37
show 2 more comments
up vote 8 down vote

BigInteger.valueOf(1695609641).toByteArray()

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up vote 4 down vote

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;
}
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up vote 2 down vote 
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;
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up vote 1 down vote

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.

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up vote 0 down vote 
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.

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up vote 0 down vote 
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;
}
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