casting a Java array

Question

i'm looking to cast an int array to a double one.

so, when i have

int arr[] = {1, 2, 3};

i want to use arr, say pass it as a double[] param to a method.

what's the best way of doing this?

the cast

(double[])arr

doesn't work.

i can iterate thru arr:

double[] dblA = new double[arr.length];
int ind=0; 
for (int x:arr)
    dblA[ind++]=x;   // (double)x;

is there a better way of doing this?

System.arraycopy isn't doing it-- doesn't work on arrays of two different primitive types.

Note: saw Casting Object to Array in Java and some other discussions.

TIA.

Look here : [stackoverflow.com/questions/9710497/… [1]: stackoverflow.com/questions/9710497/… — liotims
– liotims, Commented Sep 6, 2014 at 19:45
thx for the useful notes. C does these things. a bit discomforting that Java doesn't have t on arrays. — user3880721
– user3880721, Commented Sep 6, 2014 at 19:48
"C does these things"? I don't know of any way you can do this in C without looping through the array and creating a new array by converting each integer to a double. Did I miss something in C? (If you're talking about STL algorithms in C++, I think there might be an equivalent in Java.) — ajb
– ajb, Commented Sep 6, 2014 at 19:52
@ajb System.arraycopy() doesn't have it. nothing in Arrays either. canèt think of anywhere else in the APIs whetre this can be. — user3880721
– user3880721, Commented Sep 6, 2014 at 20:03
You can cast anything to anything in C. You'll get complete rubbish but you can cast it. :) — biziclop
– biziclop, Commented Sep 6, 2014 at 20:53

skiwi · Accepted Answer · 2014-09-06 20:23:09Z

2

Using Java 7 or below there is no easy way around it, you will simply have to manually copy them over.

Using Java 8 you can do it somewhat easier (you do need to loop over the array of course) using streams like:

int[] intArray = {1, 2, 3};
double[] doubleArray = Arrays.stream(intArray)
    .mapToDouble(i -> i)
    .toArray();

This will first create an IntStream, then map it to a DoubleStream using the conversion IntToDoubleFunction which maps every int i do a corresponding double i. Lastly you collect it using toArray

answered Sep 6, 2014 at 20:23

skiwi

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1 Comment

Константин Ван Over a year ago

You can use asDoubleStream() instead: Arrays.stream(integerArray).asDoubleStream().toArray();.

Maciej Szumielewicz · Accepted Answer · 2014-09-06 22:29:47Z

1

With Java 8 there is elegant solution based on closure:

package com.java.se.stackoverflow;

import java.util.Arrays;

public class ArrayCast {

    public static void main(String[] argv) throws Exception {
        int[] inputArray = new int[]{23, 4, 5, 6, 89};
        double[] outputArray = new double[inputArray.length];
        Arrays.setAll(outputArray, inputArrayIndex -> (double) inputArray[inputArrayIndex]);

        System.out.println(Arrays.toString(outputArray));

    }

}

edited Sep 6, 2014 at 22:29

answered Sep 6, 2014 at 19:54

Maciej Szumielewicz

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6 Comments

Sotirios Delimanolis Over a year ago

What does the given IntToDoubleFunction do?

Maciej Szumielewicz Over a year ago

it converts each integer element and returns double value

Sotirios Delimanolis Over a year ago

Which integer element?

Maciej Szumielewicz Over a year ago

sorry my mistake. Given IntToDoubleFunction function gets index of each element in int array and returnes converted to double

Hot Licks Over a year ago

How is this more "elegant" than the OP's original loop? It's more obscure, for sure, if you call that "elegant", and longer.

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