Java convert 4 bytes to single variable

Question

What I am trying to do is place 4 bytes that are currently in an array into a single byte variable. For example:

public myMethod()
{
   byte[] data = {(byte) 0x03, (byte) 0x4C, (byte) 0xD6, (byte) 0x00 };
   writeData(testMethod((byte)0x4C, data));
}

public byte[] testMethod(byte location, byte[] data)
{
    byte[] response = {(byte) 0x00, (byte) 0x21, location, data);
    return response;
}

This obviously dose not work because you cannot cast byte to byte[].

Any ideas?

EDIT: There is some confusion as to what I am asking. What I am looking for is

data = (byte) 0x034CD600;

In the "testMethod".

Ortwin Angermeier · Accepted Answer · 2013-09-06 19:02:43Z

2

You could try something like that:

private static final byte[] HEADER = new byte[] { (byte) 0x00, (byte) 0x21 };

public static byte[] testMethod(byte location, byte[] data) {
    byte[] response = Arrays.copyOf(HEADER, HEADER.length + data.length + 1);
    response[HEADER.length] = location;
    System.arraycopy(data, 0, response, HEADER.length + 1, data.length);
    return response;
}

or if you are using ByteBuffers

public static ByteBuffer testMethodBB(ByteBuffer bb, byte location, byte[] data) {
    if(bb.remaining() < HEADER.length + 1 + data.length) {
        bb.put(HEADER);
        bb.put(location);
        bb.put(data);
        bb.flip();
        return bb;
    }
    throw new IllegalStateException("Buffer overflow!");
}

edited Sep 6, 2013 at 19:02

answered Sep 6, 2013 at 17:29

Ortwin Angermeier

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1 Comment

Sotirios Delimanolis Over a year ago

+1 I like the ByteBuffer solution. You can always return the backing array too.

Sotirios Delimanolis · Accepted Answer · 2013-09-06 17:31:47Z

0

Just create a byte[] big enough to store the elements from data.

public byte[] testMethod(byte location, byte[] data)
{
    byte[] response = new byte[3 + data.length];
    response[0] = (byte) 0x00;
    response[1] = (byte) 0x21;
    response[2] = location;
    for (int i = 0; i < data.length; i++) {
        response[3 + i] = data[i];
    }
    return response;
}

Use System.arraycopy() if speed is important. I find the above more understandable.

The notation

byte[] response = {(byte) 0x00, (byte) 0x21, location, date);

is, as you said, illegal. The {...} initializer only accepts variables or literals of type byte.

edited Sep 6, 2013 at 17:31

answered Sep 6, 2013 at 17:16

Sotirios Delimanolis

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3 Comments

Talls Over a year ago

That works if I am trying to place the data at separate indexes. I need to place them all in the same index.

Sotirios Delimanolis Over a year ago

@Talls I don't understand. You cannot fit 4 bytes (32 bits) into 1 byte (8 bits).

Talls Over a year ago

You are correct. I misunderstood the context of the situation.

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