Java convert Arraylist<Float> to float[]

Question

How I can do that?

I have an arraylist, with float elements. (Arraylist <Float>)

(float[]) Floats_arraylist.toArray()

it is not working.

cannot cast from Object[] to float[]

Solution 1

Loop over it yourself.

List<Float> floatList = getItSomehow();
float[] floatArray = new float[floatList.size()];
int i = 0;

for (Float f : floatList) {
    floatArray[i++] = (f != null ? f : Float.NaN); // Or whatever default you want.
}

The nullcheck is mandatory to avoid NullPointerException because a Float (an object) can be null while a float (a primitive) cannot be null at all.

In case you're on Java 8 already and it's no problem to end up with double[] instead of float[], consider Stream#mapToDouble() (no there's no such method as mapToFloat()).

List<Float> floatList = getItSomehow();
double[] doubleArray = floatList.stream()
    .mapToDouble(f -> f != null ? f : Float.NaN) // Or whatever default you want.
    .toArray();

Solution 2

You can use Apache Commons ArrayUtils.toPrimitive():

List<Float> list = new ArrayList<Float>();
float[] floatArray = ArrayUtils.toPrimitive(list.toArray(new Float[0]), 0.0F);

Solution 3

Apache Commons Lang to the rescue.

Comments

[Seva Alekseyev]

The inverse of this: stackoverflow.com/questions/2585907/…

[bestsss]

int s=list.size(); float[] a = new float[s]; for (int i=0;i<s;i++) a[i]=list.get(i);

[Saurabh]

Different primitive type, but essentially the same question: Creating a byte[] from a List<Byte>

[PawelP]

Such a bummer. That used to be so easy in C#.

[Mickael Bergeron Néron]

In days like this I hate Java.

[Hephaestus]

Link above is broken. I used the following import: import org.apache.commons.lang3.ArrayUtils;

[Galigator]

list.toArray(...) will create an intermediate array... while the simple loop over the list won't.