How to get an ObservableFloatArray from a Stream?

Question

This is nearly the same question as this one, but in the opposite direction.

I know there\'s no FloatStream in Java 8, and there\'re no many use cases f

Answer 1

Keep in mind that a Stream defines an operation rather that a storage. So for most operations, using a float provides only little benefit over double values when CPU registers are used. There might be a theoretical improvement for operations that could be accelerated using SSE or GPU, but that’s not relevant here.

So you can use a DoubleStream for that operation, the only thing you need is a collector capable of collecting a DoubleStream into a float[] array:

float[] arrayVertices = listVertices.stream()
    .flatMapToDouble(vertex->DoubleStream.of(vertex.x, vertex.y, vertex.z))
    .collect(FaCollector::new, FaCollector::add, FaCollector::join)
    .toArray();

static class FaCollector {
    float[] curr=new float[64];
    int size;
    void add(double d) {
        if(curr.length==size) curr=Arrays.copyOf(curr, size*2);
        curr[size++]=(float)d;
    }
    void join(FaCollector other) {
        if(size+other.size > curr.length)
            curr=Arrays.copyOf(curr, size+other.size);
        System.arraycopy(other.curr, 0, curr, size, other.size);
        size+=other.size;
    }
    float[] toArray() {
        if(size!=curr.length) curr=Arrays.copyOf(curr, size);
        return curr;
    }
}

This supports parallel processing, however, for an operation that merely consist of data copying only, there is no benefit from parallel processing.