Convert float[] to byte[] to float[] again

Question

So what I'm trying to do here is get a float[], convert it to byte[], send it through the network as a datagram packet and then convert it back to a byte[] at the receiving terminal.

Now I know I can convert float[] to byte[] by using the getBytes[] method. But I don't know how to reverse the conversion.

Solution 1

I think you want to make use of the ByteBuffer class, which has putFloat and getFloat methods.

Solution 2

Another way... use ByteArrayOutputStream/DataOutputStream for output

float fArr[] = ...;
ByteArrayOutputStream bas = new ByteArrayOutputStream();
DataOutputStream ds = new DataOutputStream(bas);
for (float f : fArr) 
    ds.writeFloat(f);
byte[] bytes = bas.toByteArray();

Use ByteArrayInputStream/DataInputStream for input

byte[] buffer = ...;
ByteArrayInputStream bas = new ByteArrayInputStream(buffer);
DataInputStream ds = new DataInputStream(bas);
float[] fArr = new float[buffer.length / 4];  // 4 bytes per float
for (int i = 0; i < fArr.length; i++)
{
    fArr[i] = ds.readFloat();
}

Solution 3

Use Float.floatToIntBits() to extract the bit-value of the float as an integer, then use BigInteger.toByteArray() to make a byte[]. This can be reversed using the BigInteger constructor that takes a byte[] argument, and then Float.intBitsToFloat().

Solution 4

This is more for my future reference than anything else.

public static byte[] floatToByte(float[] input) {
    byte[] ret = new byte[input.length*4];
    for (int x = 0; x < input.length; x++) {
        ByteBuffer.wrap(ret, x*4, 4).putFloat(input[x]);
    }
    return ret;
}

public static float[] byteToFloat(byte[] input) {
    float[] ret = new float[input.length/4];
    for (int x = 0; x < input.length; x+=4) {
        ret[x/4] = ByteBuffer.wrap(input, x, 4).getFloat();
    }
    return ret;
}

Can be reduced to a single line like https://stackoverflow.com/a/44104399/322017.

Solution 5

An improvement to Steven Chou's answer

final static int BYTES_IN_FLOAT = Float.SIZE / Byte.SIZE;

public static byte[] toByteArray(float[] floatArray) {
    ByteBuffer buffer = ByteBuffer.allocate(floatArray.length * BYTES_IN_FLOAT)
    buffer.asFloatBuffer.put(floatArray);
    return buffer.array();
}


public static float[] toFloatArray(byte[] byteArray) {
    float[] result = new float[byteArray.length / BYTES_IN_FLOAT];
    ByteBuffer.wrap(byteArray).asFloatBuffer().get(result, 0, result.length);
    return result;
}

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Comments

[Dawood ibn Kareem]

But that won't give you general float values, only those that represent whole numbers between 0 and 255. A float needs 4 bytes, and the floatValue method of the Byte class only works with one.

[brain56]

Thanks! I think this is it. I'll give it a go when I get the time and I'll let you know what happens.

[Lie Ryan]

@brain56: just wanted to add that if you're sending this over a network, you would want to explicitly specify an encoding instead of leaving yourself at the mercy of the platform's default encoding.

[pzo]

there is not such a method as writeFloat - your code simply doesn't compile

[ricosrealm]

thanks for pointing it out, I've updated the code with the correct adapter class in place.

[Steven Magana-Zook]

ByteBuffer also has the asFloatBuffer() method in case you do not want to extract the values individually you can chain the method calls: ByteBuffer.wrap(someByteArray).asFloatBuffer().array() to go from a byte[] to a float[]

[Dawood ibn Kareem]

@StevenMagana-Zook You could post that as an answer.

[Mohammad Kholghi]

Can use Float.BYTES instead of Float.SIZE / Byte.SIZE

[MA90]

Float.BYTES is only available from java 8+. For older version Float.SIZE / Byte.SIZE is the way to go