CODEWITHSUNDEEP
java
keshav
keshav

Reputation: 181

Java: Convert byte to integer

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

Upvotes: 16

Views: 53398

Answers (6)

MAHESH BABU.M
MAHESH BABU.M

Reputation: 1

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();
        }

Upvotes: 0

Droid Chris
Droid Chris

Reputation: 3783

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.

Upvotes: 3

DiveInto
DiveInto

Reputation: 2266

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).

Upvotes: 11

Matt Ball
Matt Ball

Reputation: 359816

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.

Upvotes: 25

Nacho Coloma
Nacho Coloma

Reputation: 7318

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.

Upvotes: 3

Chris Dodd
Chris Dodd

Reputation: 126203

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)

Upvotes: 3

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