Can the index number be specified in the ArrayList add method

[Varuna Seneviratna]

Can the index number be specified in the ArrayList add method
If the first elemnt to be added is four

   
ArrayList int il=new ArrayList<int>();
il.add(4, 4);
 
 

4 specified as the index number, which should place four in the forth place in the il ArrayList.Is this posible?

The below program uses a feature like that

  
mport java.util.*;
 

public class ArrayListMagnet
{
public static void main(String[] args)
{
 
ArrayList<String> a=new ArrayList<String>();
a.add(0,"zero");
a.add(1, "one");
a.add(2, "two");
a.add(3, "three");
printAl(a);
a.remove(2);
if(a.contains("three"))
{
a.add("four");
}
printAl(a);
 
if(a.indexOf("four") != 4)
{
a.add(4, "4.2");
}
printAl(a);
if(a.contains("two"))
{
a.add("2.2");
}
printAl(a);
 

 

}
public static void printAl(ArrayList<String> al)
{
for(String element: al)
{
System.out.print(element + " ");
System.out.print(al.indexOf(element) + "  ");
}
System.out.println(" ");
 
}
 

}
 
  

When I specified four as the index number of zero the first addition to the list the message was
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 4, Size:
0
at java.util.ArrayList.add(ArrayList.java:367)
at ArrayListMagnet.main(ArrayListMagnet.java:10)


If the index number can be specified when an element is added, what is the use if the index number can not be a choice of the programmer?


Varuna

[Joanne Neal]

You can only specify an index that is less than the number of elements already in the ArrayList, so you can only use 4 if you already have four or more elements in the list.
[ October 02, 2008: Message edited by: Joanne Neal ]

[Rob Spoor]

Originally posted by Varuna Seneviratna:

ArrayList int il=new ArrayList<int>();
il.add(4, 4);

You can't use ArrayList<int>, but ArrayList<Integer> is a very close match thanks to auto(un)boxing.

Originally posted by Joanne Neal:
You can only specify an index that is less than the number of elements already in the ArrayList

Or equal to the number of elements
If that's the case it's added to the end.