Java convert Arraylist 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[]

The inverse of this: http://stackoverflow.com/questions/2585907/is-there-a-native-java-method-to-box-an-array — Seva Alekseyev, Jan 29 '11 at 15:09
`int s=list.size(); float[] a = new float[s]; for (int i=0;i — bestsss, Jan 29 '11 at 15:11
Different primitive type, but essentially the same question: [Creating a byte\[\] from a List](http://stackoverflow.com/questions/1565483/creating-a-byte-from-a-listbyte) — finnw, Feb 01 '11 at 20:51

BalusC · Accepted Answer · 2016-04-16T17:19:29.253

43

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();

edited Apr 16 '16 at 17:19

answered Jan 29 '11 at 15:10

BalusC

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14

Such a bummer. That used to be so easy in C#. – PawelP Oct 27 '13 at 11:23
6

In days like this I hate Java. – Mickael Bergeron Néron Apr 15 '17 at 11:17

score 36 · Answer 2 · answered Jan 29 '11 at 15:15

36

You can use Apache Commons ArrayUtils.toPrimitive():

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

answered Jan 29 '11 at 15:15

dogbane

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Link above is broken. I used the following import: `import org.apache.commons.lang3.ArrayUtils;` – Hephaestus Dec 18 '18 at 23:41
list.toArray(...) will create an intermediate array... while the simple loop over the list won't. – Galigator Jul 01 '21 at 15:46

Paul Tomblin · Answer 3 · 2014-09-30T21:56:34.170

5

Apache Commons Lang to the rescue.

edited Sep 30 '14 at 21:56

answered Jan 29 '11 at 15:11

Paul Tomblin

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Java convert Arraylist to float[]

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