Java HashSet to array

Question

I'm trying to convert a HashSet to an Array of Doubles. Yes I have a main method and class defined, I've just included what I've imported as well as the code for this specific function.

This is the Error that shows up:

Ass10.java:148: error: no suitable method found for toArray(double[])
                rtrn = s.toArray(rtrn);

Here is the code:

import java.util.List;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Set;
import java.util.HashSet;


public static double[] negated(double[] a) {
        Set<Double> s = new HashSet<Double>();
        for(double x : a) {
            s.add(x);
        } for(double x : s) {
            if(s.contains(-x) == false) {
                s.remove(x);
            }
        }
        double[] rtrn = new double[s.size()];
        rtrn = s.toArray(rtrn);
        return rtrn;
        }

Essentially there is no way to case a double[] to a Double[] like there is a double to a Double and visa versa. — Sinkingpoint
– Sinkingpoint, Commented Nov 28, 2013 at 22:47

Costi Ciudatu · Accepted Answer · 2013-11-28 22:46:43Z

1

You can't use a primitive array in this scenario, as there's no auto-boxing for arrays in Java. Use a Double[] for that to work.

answered Nov 28, 2013 at 22:46

Costi Ciudatu

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Comments

Sage · Accepted Answer · 2013-11-28 22:57:22Z

1

Java collections works with reference type. The function Collection.toArray(T[] a) has a signature of generic reference type. So you will need to pass a reference type array instead of primitive array. The corresponding reference type of primitive type double is Double.

Double[] rtrn = new Double[s.size()];
rtrn = s.toArray(rtrn);

answered Nov 28, 2013 at 22:57

Sage

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Comments

peter.petrov · Accepted Answer · 2013-11-28 22:46:50Z

0

This is a compile time error, right? Try using Double[] instead of double[].

answered Nov 28, 2013 at 22:46

peter.petrov

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