How can I concatenate two float arrays in Java?

Question

Using Java 8 I am trying to concatenate two float arrays:

void f(float[] first, float[] second) {
    float[] both = ???
}

From a quick SO search, I thought I could simply follow instruction from here. So I tried:

float both[] = FloatStream.concat(Arrays.stream(first), Arrays.stream(second)).toArray();

But this does not compile as explained here. So I tried the less efficient solution and use a Stream directly:

float[] both = Stream.concat(Arrays.stream(first), Arrays.stream(second)).toArray(float[]::new);

It fails to compile from my eclipse saying:

The method stream(T[]) in the type Arrays is not applicable for the arguments  (float[])

What is the most efficient (and simple) way of concatenating two float[] arrays in Java 8 ?

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Update: obviously the whole point of the question is that I have to deal with float and not double.

Answer 1

Don't do it yourself, use System.arrayCopy() to copy both arrays into a new array of the combined size. That's much more efficient, as it uses native OS code.

Answer 2

Since there is no FloatStream and even creating an (inefficient) boxed stream out of a float array is not simple, you won’t find a stream based solution that is simpler than

static float[] f(float[] first, float[] second) {
    float[] both = Arrays.copyOf(first, first.length+second.length);
    System.arraycopy(second, 0, both, first.length, second.length);
    return both;
}

Even the option to use a parallel stream is unlikely to outweigh the raised complexity. You would need really large arrays to see a benefit.

Answer 3

Don't write your own code to do this. The problem has already been solved and tested. You should use the Apache Commons ArrayUtils class.

float[] both = ArrayUtils.addAll(first, second);

Under the covers, it has some logic for a couple of special cases where one input or the other is null, followed by two calls to System.arraycopy. But you don't need to worry about any of that.