UnSupportedOperationException

[Meena R. Krishnan]

Converting Arrays to Lists:

Changes to the returned list 'write through' to the array

Is the reverse also true?
ie. In List to Array , will the changes to the original list show up in the array.

I tried it in the following code but giving an exception. What is the reasoning behind it?

  public static void main (String[] args) {
  String[] a = {"one","two","three"};
  
  //Array to List
  
  List<String> l = Arrays.asList(a);  
  System.out.println("List returned by asList" + l);
  a[1] = "New";  //change the returned array
   System.out.println("Same list after changes to the original array : " + l);
   
   //List to Array
   String[] aa = new String[3];
   aa = l.toArray(aa);
   for(String s: aa)
   System.out.print(s + " " );
   System.out.println();
   
   //try changing the list to see if it also changes the array
   l.clear();  //or l.add() anything causes exception here
   for(String s: aa)
   System.out.println(s);

  }

[Sasha Ruehmkorf]

See the difference?
Arrays.asList and Collections.toArray

So the Arrays.asList-method is not copying an array into a new list, it gives you just a new List-view on the array. As an array-Object is of fixed size (3 elements in this case) you are not able to add a fourth element into it, neither delete one to get an array of size two. If you are not allowed to do these operations on the array, you are of course not allowed to do the same things to your List-view, as these changes would write through to the array.
Hope, that helps.

[anil kumar]

Hi

Adding some more to Sasha

We can't call add and remove on that list(Because it is fixed) but we can
call get or set methods.

Thanks
Anil Kumar
[ May 21, 2007: Message edited by: anil kumar ]

[Meena R. Krishnan]

Thanks to you both!.

I never analyzed the name asList() and toArray(), nice to know.

Also, I never knew that only get and set are allowed with the list returned thro' Arrays.toList. I'm glad I asked.