Why FloatBuffer instead of float[]?

Question

I've been using FloatBuffers in my Android code for a while (copied it from some opengles tutorial), but I cannot understand exactly what this construct is and why it is needed.

For example this code (or similar) I see in many many peoples' code and android tutorials:

float[] vertices = ...some array...

ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length * 4); 
vbb.order(ByteOrder.nativeOrder());    // use the device hardware's native byte order
FloatBuffer fb = vbb.asFloatBuffer();  // create a floating point buffer from the ByteBuffer
fb.put(vertices);    // add the coordinates to the FloatBuffer
fb.position(0);      // set the buffer to read the first coordinate

This seems awfully verbose and messy for something which as far as I can tell is just a fancy wrapper around of an array of floats.

Questions:

• What is the justification for this type of class (ByteBuffer, FloatBuffer), as opposed to any other kind of collection or simple array of floats?

• What's the idea behind creating a ByteBuffer before converting it into a FloatBuffer?

Answer 1

The main reason is performance: ByteBuffers and the other NIO classes enable accelerated operations when interfacing with native code (typically by avoiding the need to copy data into a temporary buffer).

This is pretty important if you are doing a lot of OpenGL rendering calls for example.

The reason for creating a ByteBuffer first is that you want to use the allocateDirect call to create a direct byte buffer, which benefits from the accelerated operations. You then create a FloatBuffer from this that shares the same memory. The FloatBuffer doesn't itself have an allocateDirect method for some reason, which is why you have to go via ByteBuffer.