Java: Convert byte to integer

Question

I need to convert 2 byte array ( byte[2] ) to integer value in java. How can I do that?

This question could use some clarification. As it stands now, we will only see what you mean by which answer you select. — Victor Zamanian, Dec 20 '10 at 18:45
Does this answer your question? [Read two bytes into an integer?](https://stackoverflow.com/questions/4768933/read-two-bytes-into-an-integer) — David Krell, May 24 '23 at 11:00

score 26 · Answer 1 · edited May 23 '17 at 12:09

26

You can use ByteBuffer for this:

ByteBuffer buffer = ByteBuffer.wrap(myArray);
buffer.order(ByteOrder.LITTLE_ENDIAN);  // if you want little-endian
int result = buffer.getShort();

See also Convert 4 bytes to int.

edited May 23 '17 at 12:09

Community

1
1

answered Dec 20 '10 at 18:43

Matt Ball

354,903
100
647
710

1

Thank you this worked. Will ByteBuffer takes care of signed and unsigned bytes? – keshav Dec 20 '10 at 19:54
@keshav: what do you mean? There is no such thing as a "signed" or "unsigned" byte. A byte is just a group of `0` s and `1` s; the **only** meaning is in how you interpret those numbers. – Matt Ball Dec 20 '10 at 20:13
@Matt: Once the conversion is done, if the converted number is negative ( say -100 ), will I see it as -100? – keshav Dec 20 '10 at 20:33
@keshav: why don't you try it and see? :) Honestly - I don't know without testing it myself. – Matt Ball Dec 20 '10 at 20:36
1

@keshav: I tested it. `ByteBuffer` will handle this correctly. That is, **iff** the bytes represent a negative number, then this code will output a negative `int`. Demos: [here](http://ideone.com/MUe5p) and [here](http://ideone.com/xwBIW). Remember, it's only negative if the most significant (leftmost) bit is `1`. – Matt Ball Dec 20 '10 at 21:19
1

This won't work, as `+` has higher precedence than `<<`, so `a << 8 + b` is the same as `a << (8 + b)` which is not at all what you want. In addition, `byte` in java is signed, so bad things will happen if the low-order byte is negative. – Chris Dodd Dec 27 '10 at 23:52
This answer should be split, because the first part is wrong, while the ByteBuffer part is nice and clean, and actually works. – user1338062 Sep 18 '13 at 16:54
@MattBall yep, upvoted! I actually got bitten by the wrong part, although I wrote it myself :) – user1338062 Sep 18 '13 at 19:32

DiveInto · Answer 2 · 2013-11-21T05:59:26.443

In Java, Bytes are signed, which means a byte's value can be negative, and when that happens, @MattBall's original solution won't work.

For example, if the binary form of the bytes array are like this:

1000 1101 1000 1101

then myArray[0] is 1000 1101 and myArray[1] is 1000 1101, the decimal value of byte 1000 1101 is -115 instead of 141(= 2^7 + 2^3 + 2^2 + 2^0)

if we use

int result = (myArray[0] << 8) + myArray[1]

the value would be -16191 which is WRONG.

The reason why its wrong is that when we interpret a 2-byte array into integer, all the bytes are unsigned, so when translating, we should map the signed bytes to unsigned integer:

((myArray[0] & 0xff) << 8) + (myArray[1] & 0xff)

the result is 36237, use a calculator or ByteBuffer to check if its correct(I have done it, and yes, it's correct).

score 3 · Answer 3 · answered Aug 14 '13 at 09:06

3

Also, if you can use the Guava library:

Ints.fromByteArray(0, 0, myArray[1], myArray[0]);

It was worth mentioning since a lot of projects use it anyway.

answered Aug 14 '13 at 09:06

Nacho Coloma

7,070
2
40
43

score 3 · Answer 4 · answered Oct 15 '14 at 16:46

3

Simply do this:

return new BigInteger(byte[] yourByteArray).intValue();

Works great on Bluetooth command conversions etc. No need to worry about signed vs. unsigned conversion.

answered Oct 15 '14 at 16:46

Droid Chris

3,455
28
31

Note there's a constructor in this class where you can manually specify you wish to handle unsigned values. – brunch875 Jun 29 '19 at 12:08

score 3 · Answer 5 · answered Dec 20 '10 at 18:45

Well, each byte is an integer in the range -128..127, so you need a way to map a pair of integers to a single integer. There are many ways of doing that, depending on what you have encoded in the pair of bytes. The most common will be storing a 16-bit signed integer as a pair of bytes. Converting that back to an integer depends on whether you store it big-endian form:

(byte_array[0]<<8) + (byte_array[1] & 0xff)

or little endian:

(byte_array[1]<<8) + (byte_array[0] & 0xff)

score 0 · Answer 6 · edited Sep 17 '19 at 06:17

import java.io.*;
public class ByteArray {

    public static void main(String[] args) throws IOException {
        File f=new File("c:/users/sample.txt");
        byte[]b={1,2,3,4,5};
        ByteArrayInputStream is=new ByteArrayInputStream(b);
        int i;
        while((i=is.read())!=-1) {
            System.out.println((int)i); 
            FileOutputStream f1=new FileOutputStream(f);
            FileOutputStream f2=new FileOutputStream(f);
            ByteArrayOutputStream b1=new ByteArrayOutputStream();
            b1.write(6545);
            b1.writeTo(f1);
            b1.writeTo(f2);
            b1.close();
        }

Java: Convert byte to integer

6 Answers6

Linked