ClassCastException ArrayList->List

[gianni ipez]

Hello,
a simple question for you.

<code>
import java.util.*;
public class TestArrayList {
public static void main(String[] args) {

String[] as = {"one","two","three","four"};
ArrayList <String> al;
al = (ArrayList)Arrays.asList(as);
al.set(2,"another number");

Iterator<String> i = al.iterator();
while (i.hasNext()) {
System.out.println(i.next());
}

for(String temp : as){
System.out.println(temp);
}

}
}
</code>

This class raises a ClassCastException at line
al = (ArrayList)Arrays.asList(as);

I thought that I could cast because "ArrayList instanceof List" is true(List is the type returned by Arrays.asList(array))

Please, where am I wrong?
Thanks,
Gianni

[Keith Lynn]

The Arrays.asList method simply returns a List, not necessarily an ArrayList.

[gianni ipez]

This clarify, thanks.
But then another question:
List is an interface, so it doesn't provide implementations of get and set method, am I right?
So how can we invoke get and set methods directly from a List?
example:

 public class TestArray {
 
/**
 * @param args
 */
public static void main(String[] args) {
// TODO Auto-generated method stub
String[] s = {"one", "two", "three","four"};
List l = Arrays.asList(s);
System.out.println(l.get(1));
 

}
 
}   

Thank you !
Gianni

[Krishna Potluri]

Hi ipez,
Because al accepts only strings while casting

___________________________________________________
al = (ArrayList)Arrays.asList(as);
ArrayList <String> al;
___________________________________________________

do like this:

al = (ArrayList<String> Arrays.asList(as);

I am not sure but i hope it works.

Thanks,
Kris.

[swarna dasa]

It passes back a list inteface, hence you can call methods present in List (polymorphism).

Add the following line
System.out.println(al.getClass());

what you get is
class java.util.Arrays$ArrayList

Obviously it is not an java.util.ArrayList but an inner private class ArrayList in java.util.Arrays.

[gianni ipez]

thank you!
another little java miracle.