saving data into arraylist in a loop

Question

I have a for loop which execute 1000 times ! and I want to save the result of each iteration into an arraylist but it does not save the data from the last iteration ! it just clear the whole arraylist in every iteration and add new items to that !

how should I save the whole data ? I would not add any code because it's really complicated and really hard to explain what's going on in the loop . I want to generally know how to solve the problem and be able to save the whole data

Make sure you're not creating a new list every iteration! Learn how to create a minimal usecase that demonstrates the behavior! We can't really address the problem without knowing what your code does! — Dave Newton
– Dave Newton, Commented Jun 12, 2012 at 12:43
You're going to need to include an extract of your code at least. It's going to be like playing Pin the Tail on the Donkey in the Mariana Trench with a squid attached to your face otherwise. — Jeff Watkins
– Jeff Watkins, Commented Jun 12, 2012 at 12:43
Your question is very unclear, if it is as simple as it sounds, then just inititalize the array outside the loop and keep adding to it! i dont see the big deal here! Post the code, and help us help you! — shams.haq
– shams.haq, Commented Jun 12, 2012 at 12:44
actually the code is in processing.js which use java language and I need someone who knows that! — melisa zand
– melisa zand, Commented Jun 12, 2012 at 12:47
Doesn't matter! We can't just keep guessing! We have no idea what you're doing! What you're doing in the loop is irrelevant, what matters is how/where you create the list, and how you're adding data to it. — Dave Newton
– Dave Newton, Commented Jun 12, 2012 at 12:49

Hans Z · Accepted Answer · 2012-06-12 12:42:26Z

2

Declare your ArrayList outside of your for loop.

Like so

ArrayList results = new ArrayList();

for (int i = 0; i < 10000; ++i){
    int result = myFunction(i);
    results.add(result);
}

answered Jun 12, 2012 at 12:42

Hans Z

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Comments

Autar · Accepted Answer · 2012-06-12 12:43:11Z

2

I would need your code to understand more precisely where does the problem come from but I think it may be because you create a new ArrayList within the loop.

Your code should look like this :

List list = new ArrayList();
for(int i = 0; i < 1000; i++) {
    data = ...
    list.add(data);
}

answered Jun 12, 2012 at 12:43

Autar

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Comments

amicngh · Accepted Answer · 2012-06-12 12:55:28Z

0

Create a Empty ArrayList object out side the for loop.get your object in for loop and add it to list.

List<YourClass> list=new ArrayList<YourClass>();

    for(int i=0;i <1000;i++)
    {
        obj=new YourClass();
        list.add(obj);
    }

answered Jun 12, 2012 at 12:55

amicngh

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1 Comment

Dave Newton Over a year ago

How does this add useful information not already contained in the two existing answers?

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