Conversion of Array into List

[Pradeep Balasubramanian]

For the code provided below,

package scjp5_0.collections;
 
import java.util.Arrays;
import java.util.List;
 
public class ArrayToListConvertor {

public static void main(String[] args) {
try {
Integer numb[] = {1,23,32,323,234,234,23,51,24,52,85,521,21065,5125,414,54,485,55};
 
List numbList = Arrays.asList(numb);
 
System.out.println(numbList);
 
for(Integer i : numb) {
System.out.print(i+"   ");
}

System.out.println("\nSize of the array : " + numbList.size());
System.out.println("Integer @ tenth position of the array : " + numbList.get(10));
numbList.add(32);
System.out.println(numbList);
 
}
catch(Exception e){
e.printStackTrace();
}

}
}

why do we get the Runtime Exception.

while all the methods of List Interface are accessible by the List(converted
from Array), why is it not possible to add any new elements into the new Converted List.

Please Explain....

[Paul Somnath]

If you goto the API, ou would find this:
Returns a fixed-size list backed by the specified array. (Changes to the returned list "write through" to the array.)
So this means that the list is fixed-size and hence you cannot add to it.
However the list is synchronized with the array, this means that if you change any element in the array, same would be reflected in the list.
You can do this by:

numbList.set(1, 111);
System.out.println(numbList);
for (Integer i : numb)
{
System.out.print(i + "   ");
}

[Pradeep Balasubramanian]

Now I am clear

Also,
Once the length of array is specified , its size cannot be changed later.

Thank you, for pointing the error made by me.

[ September 16, 2008: Message edited by: Pradeep Balasubramanian ]

[Paul Somnath]

That is so obvious.
When you say:

Integer numb[] ={ 1, 23, 32, 323, 234, 234, 23, 51, 24, 52, 85, 521, 21065,
5125, 414, 54, 485, 55 };

You define the size of the array at compile time and cannot change it at runtime. Thats is what lists are for.