list and array

[hari harann]

   
import java.util.*;
class atol
{
public static void main(String args[])
{
List<Integer> l=new ArrayList<Integer>(); //1
l.add(5);
l.add(235);
l.add(45);
l.add(276);
for(Integer i:l)
System.out.println(i);//2
Integer a1[]=new Integer[5];
a1=l.toArray(a1);     //3
l.set(1,99);//4
System.out.println("--------------------\n");
for(Integer i:l)
System.out.println(i);//5
System.out.println("--------------------\n");
System.out.println(a1[1]);//6
}
}
 

1)created a list
2)printed the list
2)created an array and changed the list to array
4)altered the first element of list
5)change is reflected in the list
6)BUT NOT IN THE ARRAY. THE SAME OLD VALUE IS PRINTED HERE. it should have been changed in the array, when i change the element in the list..???

can anybody explain why is it so??

[Ulf Dittmer]

it should have been changed in the array, when i change the element in the list..???

No. The array that gets created by toArray is independent of the original List. It contains the same objects, but it will not be updated if the List is updated (the List does not know about the array).

If you look at the source code of ArrayList.toArray you will see that there is no connection between the two.

[George Gates]

Hari Harann,

Good discovery.

The book (K&B) states that only when you use asList(),any change in one (array or list) also gets updated in the other.

This is however not true for toArray(). This exception is not mentioned in the book though.