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Index › Programming Questions & Help › Syntax Questions › get or toArray to copy floats from ArrayList

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get or toArray to copy floats from ArrayList (Read 1516 times)

adnil

get or toArray to copy floats from ArrayList
Jul 22^nd, 2009, 1:44pm

Hi,

I am adding a number of floats to an ArrayList, which need to copy into an array later. Currently I am doing it with this line of code.

float xPosCount[k] = ((Float)thatXPos.get(k)).floatValue();

As such it works, but it seems that it doesn't copy them in the order they were in the Arraylist but sorts them into - smallest value first - highest value last. Is that correct? I was trying to use toArray() instead and put my code like that

float xPosCount[k] = ((Float)thatXPos.toArray(k)).floatValue();

but this doesnt work. I tried lots of other things but cant work it out. Some help would be great.

PhiLho

Re: get or toArray to copy floats from ArrayList
Reply #1 - Jul 22^nd, 2009, 2:54pm

I fear I don't understand how the first line can work, I haven't tried but I would bet you would get a syntax error there (in the declaration float xPosCount[k]).
I don't see either how your data gets magically sorted...

The second line is even more perplexing...
Perhaps something like:
float[] xPosCount = new float[thatXPos.size()]; thatXPos.toArray(xPosCount);
could work (untested).

[EDIT] Fixed hasted code against syntax errors, but it doesn't work. Sad

« Last Edit: Jul 23^rd, 2009, 1:11am by PhiLho »

alvaro

Re: get or toArray to copy floats from ArrayList
Reply #2 - Jul 22^nd, 2009, 3:09pm

Like PhiLo says, things don't get sorted automatically. To convert an ArrayList into an Array of floats, you could do it like this:

Code:


ArrayList list = new ArrayList();

..add numbers into list...

/* Convert ArrayList into Array of Objects */  
Object[] temp = list.toArray();

/* create an empty Array of floats */
float[] fList = new float[list.size()];

for (int i = 0; i < temp.length; i++) {
    /* 
    First Cast each Object into Float.
    There is a second --implicit-- cast 
    from object Float to type float,
    this happens automatically.
    */
    fList[i] = (Float) temp[i];
  }

PhiLho

Re: get or toArray to copy floats from ArrayList
Reply #3 - Jul 23^rd, 2009, 1:16am

alvaro is right, although I would have used (float) instead of (Float).
My code above doesn't work, Java fails to convert an ArrayList of boxed primitive types to an array of this primitive type...
A variant of alvaro's code:
Code:

ArrayList thatXPos = new ArrayList();
// Use autoboxing feature of Java 1.5
for (int i = 0; i < 10; i++) thatXPos.add(random(50));

int len = thatXPos.size();

float[] xPosCount = new float[len];

Float[] fa = new Float[len];
thatXPos.toArray(fa);
for (int i = 0; i < len; i++)
{
  // Using auto unboxing
  xPosCount[i] = fa[i];
}

for (int i = 0; i < len; i++) println(xPosCount[i]);

Hey, auto(un)boxing is one of the rare Java 1.5 features we can use (since it doesn't change syntax), so I won't miss it! Wink

adnil YaBB Newbies Offline Posts: 28	Re: get or toArray to copy floats from ArrayList Reply #4 - Jul 29^th, 2009, 4:35am thanks, very helpful, got it working.

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