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(){

}

Read this http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#toArray%28T[]%29 — noMAD
– noMAD, Commented Apr 21, 2012 at 20:39

Jonathan · Accepted Answer · 2012-04-21 21:54:18Z

2

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;
}

edited Apr 21, 2012 at 21:54

answered Apr 21, 2012 at 20:51

Jonathan

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4 Comments

Andres F. Over a year ago

Or better yet, just use ArrayList.toArray() ;)

Jonathan Over a year ago

.toArray() doesn't convert an ArrayList of Double into an array of the primitive double type.

Andres F. Over a year ago

Ouch! You're right. Maybe a Double[] is equally useful for the OP, though.

David Harkness Over a year ago

This will throw a NullPointerException if any of the elements is null.

Hüseyin Z. · Accepted Answer · 2012-04-21 20:44:14Z

1

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

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

answered Apr 21, 2012 at 20:44

Hüseyin Z.

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2 Comments

Andres F. Over a year ago

@user1348759 What do you mean "it does not work"? It does work.

Andres F. Over a year ago

It's true toArray() doesn't convert to an array of double[]. But it does convert to Double[], is that useful to you?

Tomasz Nurkiewicz · Accepted Answer · 2012-04-21 20:53:27Z

1

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);

answered Apr 21, 2012 at 20:53

Tomasz Nurkiewicz

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Comments

Louis Wasserman · Accepted Answer · 2012-04-21 22:56:27Z

0

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.)

answered Apr 21, 2012 at 22:56

Louis Wasserman

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