converting bytes to int in Java

Question

I need to convert 2 bytes (2's complement) into an int in Java code. how do I do it?

toInt(byte hb, byte lb)
{

}

do you want to implement it by yourself because you have a specific task by your teacher or something? Or do you just want to use the build-in-Java class? — TheChange
– TheChange, Commented Jun 23, 2010 at 20:51
if the build-in-java class has a method to convert 2 bytes into an integer, sure let me know. — user121196
– user121196, Commented Jun 23, 2010 at 20:54
possible duplicate of [Convert 4 bytes to int ](stackoverflow.com/questions/2383265/convert-4-bytes-to-int) — OscarRyz
– OscarRyz, Commented Jun 23, 2010 at 20:56
Perhaps consider why you're passing around raw bytes? You might solve this problem easily by going to SO, but this is indicative of bigger problems. What is this int? Why must it be in bytes? What alternatives are there for persisting this data in another form? — corsiKa
– corsiKa, Commented Jun 23, 2010 at 21:05

Yann Ramin · Accepted Answer · 2010-06-23 20:51:57Z

15

return ((int)hb << 8) | ((int)lb & 0xFF);

Correct operation in all cases is left as an exercise for the student.

answered Jun 23, 2010 at 20:51

Yann Ramin

33.2k3 gold badges63 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Mark Peters Over a year ago

Those casts are both redundant.

Andras Balázs Lajtha Over a year ago

It should be noted that this solution works only with signed short integer representation, and won't be appropriate to decode TCP headers where ports are represented in an unsigned format.

j2gl Over a year ago

If you don't want to lose precision, you need to do it with "& 0xFF ". Like this: return (hb & 0xFF) << 8 | (lb & 0xFF);

maerics · Accepted Answer · 2010-06-24 00:14:36Z

11

You can also use the ByteBuffer class:

public int toInt(byte hb, byte lb) {
    ByteBuffer bb = ByteBuffer.wrap(new byte[] {hb, lb});
    return bb.getShort(); // Implicitly widened to an int per JVM spec.
}

This class might be helpful if you're decoding a lot of data.

edited Jun 24, 2010 at 0:14

answered Jun 23, 2010 at 21:06

maerics

157k47 gold badges277 silver badges299 bronze badges

4 Comments

corsiKa Over a year ago

But if the two bytes are in 2's compliment, wouldn't that make the first byte of hb the sign bit? So your new byte[]{a,b,c,d} would be a= hb & 0x80; b=0; c= hb & 0x7F; d= lb;? I could be off base here.

maerics Over a year ago

Good point, the first bit of hb should be pulled to the left-hand side of a, so my solution probably isn't what he's looking for. I just wanted to point out the ByteBuffer class...

finnw Over a year ago

Use getShort instead of getInt. When you cast the resulting short to an int it will be sign-extended giving the correct result.

maerics Over a year ago

@finnw: great idea, why didn't I think of that? =)

AZ_ · Accepted Answer · 2014-01-22 04:20:04Z

Usage:

public class Test {

    public static void main(String[] args) {
        byte[] b = new byte[] { -83, 0, 0, 0 };

        int i = GattUtils.getIntValue(b, GattUtils.FORMAT_UINT32, 0);

        System.out.println(i); //will print 173
    }


public class GattUtils {
    public static final long leastSigBits = 0x800000805f9b34fbL;

    public static final int FIRST_BITMASK = 0x01;
    public static final int SECOND_BITMASK = FIRST_BITMASK << 1;
    public static final int THIRD_BITMASK = FIRST_BITMASK << 2;
    public static final int FOURTH_BITMASK = FIRST_BITMASK << 3;
    public static final int FIFTH_BITMASK = FIRST_BITMASK << 4;
    public static final int SIXTH_BITMASK = FIRST_BITMASK << 5;
    public static final int SEVENTH_BITMASK = FIRST_BITMASK << 6;
    public static final int EIGTH_BITMASK = FIRST_BITMASK << 7;

    public static final int FORMAT_UINT8 = 17;
    public static final int FORMAT_UINT16 = 18;
    public static final int FORMAT_UINT32 = 20;
    public static final int FORMAT_SINT8 = 33;
    public static final int FORMAT_SINT16 = 34;
    public static final int FORMAT_SINT32 = 36;
    public static final int FORMAT_SFLOAT = 50;
    public static final int FORMAT_FLOAT = 52;

    public static UUID toUuid(String uuidString) {
        return UUID.fromString(uuidString);
    }

    public static UUID toUuid(long assignedNumber) {
        return new UUID((assignedNumber << 32) | 0x1000, leastSigBits);
    }

    public static String toUuid128(long assignedNumber) {
        return toUuid(assignedNumber).toString();
    }

    public static String toUuid16(int assignedNumber) {
        return Integer.toHexString(assignedNumber);
    }

    public static Integer getIntValue(byte[] value, int format, int position) {
        if (value == null)
            return null;
        if (position + (format & 0xF) > value.length)
            return null;
        switch (format) {
        case FORMAT_UINT8:
            return Integer.valueOf(value[position] & 0xFF);
        case FORMAT_UINT16:
            return Integer.valueOf(add(value[position], value[(position + 1)]));
        case FORMAT_UINT32:
            return Integer.valueOf(add(value[position], value[(position + 1)], value[(position + 2)], value[(position + 3)]));
        case FORMAT_SINT8:
            return Integer.valueOf(signed(value[position] & 0xFF, 8));
        case FORMAT_SINT16:
            return Integer.valueOf(signed(add(value[position], value[(position + 1)]), 16));
        case FORMAT_SINT32:
            return Integer.valueOf(signed(add(value[position], value[(position + 1)], value[(position + 2)], value[(position + 3)]), 32));
        }
        return null;
    }

    public static Float getFloatValue(byte[] value, int format, int position) {
        if (value == null)
            return null;
        if (position + (format & 0xF) > value.length)
            return null;
        int i;
        int mantissa;
        int exponent;
        switch (format) {
        case FORMAT_SFLOAT:
            i = value[(position + 1)];
            position = value[position];
            mantissa = signed((position & 0xFF) + ((i & 0xFF & 0xF) << 8), 12);
            exponent = signed((i & 0xFF) >> 4, 4);
            return Float.valueOf((float) (mantissa * Math.pow(10.0D, exponent)));
        case FORMAT_FLOAT:
            exponent = value[(position + 3)];
            mantissa = value[(position + 2)];
            i = value[(position + 1)];
            position = value[position];
            return Float.valueOf((float) ((format = signed((position & 0xFF) + ((i & 0xFF) << 8) + ((mantissa & 0xFF) << 16), 24)) * Math.pow(10.0D, exponent)));
        }
        return null;
    }

    public static String getStringValue(byte[] value, int position) {
        if (value == null)
            return null;
        if (position > value.length)
            return null;
        byte[] arrayOfByte = new byte[value.length - position];
        for (int i = 0; i != value.length - position; i++) {
            arrayOfByte[i] = value[(position + i)];
        }
        return new String(arrayOfByte);
    }

    private static int add(byte byte1, byte byte2) {
        return (byte1 & 0xFF) + ((byte2 & 0xFF) << 8);
    }

    private static int add(byte byte1, byte byte2, byte byte3, byte byte4) {
        return (byte1 & 0xFF) + ((byte2 & 0xFF) << 8) + ((byte3 & 0xFF) << 16) + ((byte4 & 0xFF) << 24);
    }

    private static int signed(int value, int length) {
        if ((value & 1 << length - 1) != 0)
            value = -1 * ((1 << length - 1) - (value & (1 << length - 1) - 1));
        return value;
    }

    /**
     * Convert hex byte array from motorola API to byte array.
     * 
     * @param hexByteArray
     * @return
     */
    public static byte[] hexByteArrayToByteArray(byte[] hexByteArray) {
        return hexStringToByteArray(new String(hexByteArray));
    }

    /**
     * Convert string from motorola API to a byte array.
     * 
     * @param hexString
     * @return
     */
    public static byte[] hexStringToByteArray(String hexString) {
        int len = hexString.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(hexString.charAt(i), 16) << 4) + Character.digit(hexString.charAt(i + 1), 16));
        }
        return data;
    }
}

Bill the Lizard · Accepted Answer · 2010-06-23 20:59:26Z

-1

public int toInt(byte hb, byte lb)
{
    return ((int)hb)<<8 + lb;
}

edited Jun 23, 2010 at 20:59

Bill the Lizard

407k213 gold badges579 silver badges892 bronze badges

answered Jun 23, 2010 at 20:52

luke

14.9k6 gold badges51 silver badges58 bronze badges

2 Comments

user121196 Over a year ago

is this answer the same as the one by theatrus?

Andras Balázs Lajtha Over a year ago

Edited the answer, the solution was to add parentheses around the << operator, hope it'll be approved soon and others won't spend a day debugging the code that uses this snippet :)

Oz Shabat · Accepted Answer · 2020-04-07 13:29:45Z

-1

For those of you who are looking for the Little Endian value:

int num = ByteBuffer.wrap(b, 0, 2).order(LITTLE_ENDIAN).char.toInt()

answered Apr 7, 2020 at 13:29

Oz Shabat

1,65218 silver badges18 bronze badges

Collectives™ on Stack Overflow

converting bytes to int in Java

5 Answers 5

3 Comments

4 Comments

Comments

2 Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

3 Comments

4 Comments

Comments

2 Comments

Comments

Linked

Related