How to convert ArrayList to Array

Question

I have a Person class

 public class Person 
        {
          private int age;
          private String first;
          private boolean valid;
        }

I have created an ArrayList of Person objects

ArrayList<Person> valid = new ArrayList<Person>();
        for(Person p : in)
        {
         valid.add(p);
        }

Now I want to convert this ArrayList to an array; I have tried this:

Person[] people = (Person[]) valid.toArray();

but this is throwing exception

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Lcom.net.Person;

Antoniossss · Accepted Answer · 2015-09-22 14:09:02Z

6

you have to do something like this

Person[] people = valid.toArray(new Person[valid.size()]);

answered Sep 22, 2015 at 14:09

Antoniossss

32.7k7 gold badges67 silver badges119 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Antoniossss Over a year ago

sure it does:) glad I could help

user1668782 Over a year ago

@Antoniossss- have put 0 instead of valid.size() still working I don't understand How? Person[] people = valid.toArray(new Person[0]);

Antoniossss Over a year ago

toArray will allocate new array if the one you will pass is not large enught to fit all contents. What happend with accepted answer ??

user1668782 Over a year ago

I have accepted don't know how it was changed, Anyway I had accepted again

Ajay · Accepted Answer · 2015-09-22 14:10:29Z

1

You can't cast an Object[] to a Person[]. The toArray method needs to return the right type. There's an overloaded version of that method which takes an array of your type.

Person[] people = valid.toArray(new Person[valid.size()]);

http://docs.oracle.com/javase/7/docs/api/java/util/Collection.html#toArray(T[])

answered Sep 22, 2015 at 14:10

Ajay

7635 silver badges17 bronze badges

Comments

Tokay · Accepted Answer · 2015-09-22 14:10:59Z

1

Can you try something like this:

Person[] people = valid.toArray(new Person[valid.size()]);

answered Sep 22, 2015 at 14:10

Tokay

1572 silver badges15 bronze badges

Comments

dimo414 · Accepted Answer · 2015-09-22 14:14:36Z

As you can see in the Javadocs, List.toArray() returns an Object[], so the list's generic type information is lost. That's why your cast doesn't work.

If you need to preserve the generic information, you must use the alternative toArray() method which takes an array of the desired type (because you could, for instance, want to turn a List<String> into a List<CharSequence> and so on).

All you need to do is pass an empty array of the desired type, e.g.:

list.toArray(new Person[]{});

However this is a little wasteful, as it forces the toArray() method to construct a new array of the appropriate size at runtime (via reflection). If instead you pass in an array that is already large enough, it will reuse that array avoiding the reflection and extra allocation.

list.toArray(new Person[list.size()]);

Collectives™ on Stack Overflow

How to convert ArrayList to Array

4 Answers 4

4 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

4 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related