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up vote 1 down vote favorite 
ArrayList<Student> alist = new ArrayList();
// object type is student
//arraylist contains student objects        
Student[] arr= new Student[un.size()];

for(int i = 0; i <= alist .size(); i++){
    them[i] = arr.get(i);
}

What I want to do is to create an array of students without getting the array out of bounds exception.

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i think err is you have un object for size . use alist.size(). plus api method is there see Stendika's answer –  tgkprog Jan 1 at 14:46

5 Answers 5

up vote 3 down vote

Arrays are zero-based in Java (and most languages). If you have an array of size N, the indexes will be from [0, N-1] (Total size of N).

i <= alist .size()

should be

i < alist .size()
   ↑
 No "="

Why don't you simply use toArray?

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@ZouZou Indeed. Thanks, fixed the link :) –  Maroun Maroun Jan 1 at 14:26
up vote 1 down vote

You are very close. Your for loop condition says to loop as long as i is less than or equal to alist.size(). If you do that, you'll always run one over.

For example, if you only have one item in alist, your size will be 1, but you really only want to loop until 0.

Change this:

for(int i = 0; i <= alist.size()  ; i++)

To this:

for(int i = 0; i <  alist.size()  ; i++)
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up vote 1 down vote

All you really need is to say is them = alist.toArray(new Student[them.length]). This will simply copy the data over.

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up vote 0 down vote 
ArrayList<Student> alist = new ArrayList();
// object type is student
//arraylist contains student objects        
Student[] arr= new Student[un.size()];
alist.toArray(arr);
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up vote 0 down vote

You can try like this also, All above ans are correct but this is simple and easy

String[] arr = alist.toArray(new Student[un.size()]);

list.toArray return an array containing all of the elements in this collection

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