convert a LongBuffer/IntBuffer/ShortBuffer to ByteBuffer

Question

I know a quick way to convert a byte/short/int/long array to ByteBuffer, and then obtain a byte array. For instance, to convert a byte array to short array I can do:

byte[] bArray = { 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0 };

ByteBuffer bb = ByteBuffer.wrap(byteArray);
ShortBuffer sb = bb.asShortBuffer();
short[] shortArray = new short[byteArray.length / 2];
sb.get(shortArray);

produces a short array like this: [256, 0, 0, 0, 256, 0, 0, 0].

How can I do the inverse operation using java.nio classes?

Now I am doing this:

shortArray[] = {256, 0, 0, 0, 256, 0, 0, 0};
ByteBuffer bb = ByteBuffer.allocate(shortArray.length * 2);
for (short s : shortArray) {
    bb.putShort(s);
}
return bb.array();

And I obtain the original [1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0] byte array. But I want to use a method like ShortBuffer.asByteBuffer(), not a manual loop to do it.

I have found a request to Sun of 2001, but they did not accept it ;-((

Answer 1

What about this? :

    bb.asShortBuffer().put(shortArray);

Then bb contains your data.

Full code:

public class Test {
    public static void main(final String args[]) {
        short[] arr = { 256, 0, 0, 0, 256, 0, 0, 0 };
        for (byte b : F(arr)) {
            System.out.print(b);
        }
    }

    public static byte[] F(short[] arr) {
        java.nio.ByteBuffer bb = java.nio.ByteBuffer.allocate(arr.length * 2);
        bb.asShortBuffer().put(arr);
        return bb.array(); // this returns the "raw" array, it's shared and not copied!
    }
}

Answer 2

Well, in the declaration

ShortBuffer sb = bb.asShortBuffer();

AFAIK, your ShortBuffer is just a view of the original ByteBuffer. So, you could always access the original ByteBuffer variable bb and see the data as modified through your CharBuffer reference sb.

The documentation for asCharBuffer says:

[...] Changes to this buffer's content will be visible in the new buffer, and vice versa [...]