double[][] data;

public Iterator<double> iterator() {
    return new FishIterator(data);
}

private class FishIterator<double> implements Iterator<double> {
    private int x = 0, xm, y = 0, ym
    public FishIterator(double[][] data) {
        xm = data.length;
        ym = data[0].length;
    }

    public boolean hasNext() {
        return !(y == ym-1 && x == xm-1);
    }

    public double next() {
        if (++x >= xm) {
            x = 0;
            y++;
            return data[x][y];
        }
    }

    public void remove() {
        throw new UnsupportedOperationException();
    }
}