Convert ArrayList to Arrays in Java

Moe Lavigne says:

String[] countries = new String[0];

List list = new ArrayList();
list.add(“India”);
list.add(“Switzerland”);
list.add(“Italy”);
list.add(“France”);

countries = list.toArray(countries);

TinhTruong says:

You don’t have to put the list.size() to the new array, just 0 is enough because it just uses the information about the type of the return array, not the size, so the following code will work:
T [] countries = list.toArray(new T[0]);

Moe Lavigne says:

Maybe the following comment would have been better:

This is also works: T[] countries = list.toArray(new T[0]);

The \"toArray\" method automatically adjusts the size of the target array, but it must be initialized… I just use zero;

Dave says:

Thanks!
It was useful for me! :)

Hauke says:

If you use an array with the correct size within the toArray method, the result is returned within the provided array. If you use a “new T[0]” another array has to be created, that is thrown away after the type information is read.
So it is bad style to use “new T[0]”.

Frsutrated says:

If your code works then can you please explain this?

Test.java:8: generic array creation
T [] countries = list.toArray(new T[list.size()]);
^
1 error

cristian says:

thanks!!!!!!

Ahmad says:

Thank you for the great post.
Maybe, it’s too late to say this but anyway, let’s try.
About the Array to ArrayList conversion, I got error. It cannot recognize the Arrays type.
Obviously, I imported the needed classes but even the NetBeans auto-complete couldn’t help to find the reason of the error!
By a little bit searching, I figured out that the following code works fine:

String[] countries = {“India”, “Switzerland”, “Italy”, “France”};
ArrayList list = new ArrayList(Arrays.asList(countries));

Thanks,
Ahmad

ram says:

thanks

Shakeel says:

This is good way to convert ArrayList to Array

//this is Generic 
        ArrayList al = new ArrayList();
        al.add("Shakeel");
        al.add("Raj");
        
        //this is collection
        ArrayList al1 = new ArrayList();
      al1.add("Shakeel");
        al1.add("Shaan");
        al1.add("Shakeel");
        al1.add("Raj");
       
               
        
        //ArrayList to Array
        String ar[]=al.toArray(new String[al.size()]);
        ar=al.toArray(ar);
        for(int j=0;j<ar.length;j++)
        {
            System.out.println("Element of ar " + ar[j]);
        }
        System.out.println("");
        Object ar1[]=al1.toArray(new Object[al1.size()]);
        ar1=al1.toArray(ar1); 
        for(Object e:ar1)
        System.out.println("Elements of ar1 " +(String) e);

Dennis meade says:

I’ve been wanting to use .toArray() for awhile, but could never figure out the syntax.. Now I can use it. In my opinion, Sun did a terrible job of documenting generics.

Thanks

Mitul Patel says:

Thanks. Its a very useful to me.

sadhana says:

I agree with dennis.Even I couldn’t figure out the way to use toArray() in generics straight forward. This post helped to figure that out. Thank You!!!

vidyashree says:

i have one doubt see arrays can store only similar types of data if collection contain different types of data like objects thn if we convert to array hw it is converted pls tel me if u know?

Max says:

Thank you, that is very useful … I never initialized the arrays with the right size and, of course, it did not work and they used .toArray() instead, but now I know how to do it right! :)

Cvenkel Miran says:

Sorting does not work in case of string:

“Trnkoczyjeve kričistilne jagode”

note the “č” character.

I would apprecaite a tip, where to modify ColumnComparator class to get this to work.
Note, “č” comes here in alphabet: abcčdefg….

ArunM says:

Thanks Viral. Was wondering how I could convert without typecasting

Developer says:

Very Useful. Thanks for sharing info.

Laramie Crocker says:

Hi,
Thanks for your post. Small syntax error has crept into your example code on the main part of the post:

String[] countries = {“India”, “Switzerland”, “Italy”, “France”};
List list = new Arrays(Arrays.asList(countries));

This won’t compile because you can’t (and don’t want to) call new Arrays(). It is a helper class, with static functions. It is sufficient to say:

List list = Arrays.asList(countries);

Thanks,
Laramie

divy says:

Nice blog….

jay says:

this is much is enough guys…………..

int[] d = new int[list.size()];
for(int i=0;i<list.size();i++){
d[i] = list.get(i);
}

wangzhengyi says:

thank you, it’s very useful to me

Omor Faruq says:

U R great!

Chandran says:

Thanks it was helpful..

Dev says:

Thank you. Great post !!

Sateesh says:

List prepareIssueMonitorMasterList = new ArrayList();
I have some IssueMonitorMaster added to list.
Now i am converting the above list to IssueMonitorMaster[] by using below code
IssueMonitorMaster[] issueMonitorMasterArray = prepareIssueMonitorMasterList.toArray(new IssueMonitorMaster[prepareIssueMonitorMasterList.size()]);
I am getting StackOverflowError
I am struggling from 2 days can some one please help me

ivan says:

thank you so much

Naren says:

Hi, I have a need like this
InterfaceXYZ list = new ArrayList(); // I am using Java 7.

InterfaceXYZ [] countries = list.toArray(new T[list.size()]); ==> This is giving me compile time error. I want to create an array with InterfaceXYZ and return as this array. How to do it ?

T4Tester says:

How to convert int []x = {3,2,1,3,2,1,4,3,5,3} to Set ?

arun says:

Thank you.It was useful to me

Shahid Siddique says:

This makes it more clear now. thanks.