Arrays.toArray : All my knowledge collapses ...

[Cyril Bil]

Hi guys I just try this sample question :

import java.util.*;
public class ToDo {
  public static void main(String[] args) {
    String[] dogs = {"fido", "clover", "gus", "aiko"};
    List dogList = Arrays.asList(dogs);
    dogList.add("spot");
    dogs[0] = "fluffy";
     System.out.println(dogList);
     for(String s: dogs) System.out.print(s + " ");
   }
 }

I was sure at 110% that code compile and run without exception and .....

 Exception in thread "main" java.lang.UnsupportedOperationException
	at java.util.AbstractList.add(AbstractList.java:131)
	at java.util.AbstractList.add(AbstractList.java:91)
	at com.test.ToDo.main(ToDo.java:10)

I go to the API doc and see


asList(T... a) : Returns a fixed-size list backed by the specified array.


ARghhhhhhhhhhh I thinhed that the first specifities of collection vs arrays was that collections has no fixed size ... :/

So my question : is there another method to fixed size for collection, and if there is another method is it only for List, ot also for set, map etc ...

Thanks.

[Stephan van Hulst]

In the standard API? I'm not sure. You probably shouldn't care either. Just read the method documentation carefully when you use a method.

[Harsha Smith]

Yes, Arrays.asList(T...a) produces a list backed by the array. The size is fixed and also its very slow.

String [] array = {};
ArrayList<String> list = new ArrayList<String>();
Collections.addAll(list,array); //This should be your preferred choice as it runs significantly faster

[sakthi moorthy]

If you want to add or remove elements from List which was returned from Arrays.asList(dogs); method
change your code like following

List dogList = new ArrayList(Arrays.asList(dogs));

Thanks & Regards
S.Sathiya