adding a double to an ArrayList

Question

I wrote an android app that solves quadratic equations and then is supposed to graph them. The library I am using requires the data sets to be in ArrayList form. However the loop I have to create the array involves adding a double to them which you cannot do with array lists. Here is the code:

List<double[]> x = new ArrayList<double[]>();
List<double[]> values = new ArrayList<double[]>();
QuadraticActivity c = new QuadraticActivity();


x=(c.xValueArr);
values=(c.yValueArr);

for (; c.xCurrent <= c.xEnd; c.xCurrent += c.xStep) {
    double yCurrent = (c.a)*Math.pow(c.xCurrent, 2) + (c.b)*c.xCurrent + (c.c);
    c. xValueArr .add ((c.xCurrent));
    c. yValueArr .add ((yCurrent));

What error are you getting? Note that you have a List of double arrays, not a list of doubles. — Thilo
– Thilo, Commented Aug 17, 2011 at 3:12
I suggest moving line 3 to the first line and replacing the two new ArrayList.. statements with the statements in lines 6 & 7. Your code should look like this: QuadtraticActivity c = new QuadraticActivity(); List<Double> x = c.xValueArr; List<Double> values = c.yValueArr; cause the ArrayLists that you created with new are just replaced in lines 6 & 7. — cesar
– cesar, Commented Aug 17, 2011 at 3:19

cesar · Accepted Answer · 2011-08-17 03:35:33Z

1

Judging from your code, c.xValueArr and c.yValueArr are of type, double[]. If so, then just change the first 7 lines of code to this:

QuadraticActivity c = new QuadraticActivity ();
ArrayList<Double> x = Arrays.asList (c.xValueArr);
ArrayList<Double> values = Arrays.asList (c.yValueArr);

Note: You're instantiating two new ArrayLists in lines 1 and 2 but are replacing them in lines 6 and 7. Also, you'll have to add the new values inside the loop manually, as x and values don't point to the same arrays as c's arrays. A better fix would be to declare and initialize x and values after the iteration, but since you didn't include a closing }, I'm assuming you need them in the iteration.

answered Aug 17, 2011 at 3:35

cesar

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Comments

romy_ngo · Accepted Answer · 2011-08-17 03:23:23Z

1

ArrayList should work fine with Integer or Double because they are as good as other object. Note that they must have the first letter capitalized.

You should also consider Double.valueOf(double d) which returns an object of Double for your use case

answered Aug 17, 2011 at 3:23

romy_ngo

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dlev · Accepted Answer · 2011-08-17 03:17:34Z

0

Is it possible to use a subclass of Number? It wraps a value in an object. http://download.oracle.com/javase/1.4.2/docs/api/java/lang/Number.html

Try Double with a capital 'D'.

http://download.oracle.com/javase/1.4.2/docs/api/java/lang/Double.html

edited Aug 17, 2011 at 3:17

dlev

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answered Aug 17, 2011 at 3:15

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Ryan Reeves · Accepted Answer · 2011-08-17 03:17:43Z

0

Use the Double object instead of the double native type.

List<Double> x = new ArrayList<Double>();
List<Double> values = new ArrayList<Double>();

edited Aug 17, 2011 at 3:17

answered Aug 17, 2011 at 3:12

Ryan Reeves

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2 Comments

cesar Over a year ago

I didn't downvote, but removed my upvote cause I reread the post, and realized @Owen isn't using the ArrayLists he initialized. Instead, he replaces them in lines 6 & 7. @Owen's question isn't too clear though, so AFAIK, you could still be right, though.

Ryan Reeves Over a year ago

Yeah I see that now. I just answered his question about adding doubles to ArrayList and called it good.

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