a method for converting an ArrayList into an array in java

Question

Here I have

class x{
    ArrayList<Double> values;
    x() {
        values= new ArrayList<Double>();
    }

//here I want to write a method to convert my arraylis(values) in class(x) into an array to be able to use it in my program. Is there any way to do that. thx for your help.

public double [] getarray(){

} 

Answer 1

You shouldn't really need to turn an ArrayList to an array, but if you do, here's how.

public double [] getArray(){
    double[] array = new double[values.size()];
    for(int i =0;i<values.size();i++)
    {
        array[i] = values.get(i) != null ?values.get(i):  0.0;
    }
    return array;
} 

Answer 2

Your array list have a toArray() method. Try using that one like:

public double [] getarray(){
    return values.toArray();
} 

Answer 3

With a little help of Apache Commons Lang (see: ArrayUtils.toPrimitive()):

final ArrayList<Double> objList = new ArrayList<Double>();
final Double[] objArray = objList.toArray(new Double[objList.size()]);
final double[] primArray = ArrayUtils.toPrimitive(objArray);

Answer 4

If the problem is converting it to a primitive double[], and you can use Guava, then double[] Doubles.toArray(Collection<Double>) does the job just fine. (Disclosure: I contribute to Guava.)