寻找更好的方法来转换ArrayList <Double> 加倍[]数组

Question

I've been searching a solution for converting an ArrayList to a double[] array. After reading a few questions on the same issue, i figure out a solution. This is how i work now.

  public static double[] listToArray(List<Double> arr){   
  double[] result = new double[arr.size()];
  Iterator<Double> itr = arr.iterator();
  int i = 0 ; 
  while(itr.hasNext()){
      try{
          result[i] = Double.parseDouble(itr.next().toString());
          i++;
      }catch(IndexOutOfBoundsException e){
          System.out.println("OutOfBouds");
      }
  }      
  return result;
  }

This is a rather nasty way. I know there are some APIs that can do what i want. But in that case, i will bring extra complexity to my project, which is not what i want to see. Can anyone give me a better solution??

Answer 1

public static double[] listToArray(List<Double> arr){   
    double[] result = new double[arr.size()];
    int i = 0;
    for(Double d : arr) {
        result[i++] = d.doubleValue();
    }
    return result;
}

Answer 2

Well, there is: .toArray() but that will get you an array of Double objects.

Try:

ArrayList<Double> objList;
double[] primList = new double[objList.size()];
for (int i =0; i < objList.size(); ++i)
   primList[i] = objList.get(i);

Answer 3

double[] test(final List<Double> sourcelist) {
    if (sourcelist==null) {
        return null;
    }
    double[] array = new double[sourcelist.size()];
    int i = 0;
    for (Double value : sourcelist) {
        if (value == null) {
            array[i++] = 0D; // or some other null representation
        } else {
            array[i++] = value.doubleValue();
        }
    }
    return array;
}

Answer 4

Here is how Apache Commons Lang doit

org.apache.commons.lang.ArrayUtils:

    public static double[] toPrimitive(Double[] array) {
        if (array == null) {
            return null;
        } else if (array.length == 0) {
            return EMPTY_DOUBLE_ARRAY;
        }
        final double[] result = new double[array.length];
        for (int i = 0; i < array.length; i++) {
            result[i] = array[i].doubleValue();
        }
        return result;
    }