Warning in java : unchecked or unsafe operation

[hostel]

import java.util.ArrayList;
import java.util.Iterator;


public class collectionsremove
{

public static void main(String[] args)
{


ArrayList arr = new ArrayList();
String str1 = "hi";
arr.add(str1);
arr.add("hello");
arr.add("wassup");
arr.add("wazzup");
arr.add("bye");



Iterator it = arr.iterator();

while(it.hasNext() )
{

it.next();
it.remove();
}
}
}

}



when i compile this code i get warning as :
collectionsremove.java use unchecked or unsafe operation
recompile with -Xlint : unchecked for detail


how to remove this warning .

anyhow my program runs fine , how to remove

[JosAH]

Starting at Java 1.5 the Java language implements 'generics', i.e. a type can be
specified using another type. This is all a compilation feature and the Java virtual
machine didn't change for that. You are using the 'raw' type of ArrayList and the
compiler warns you for it (you can stick any type on a raw List). After compilation
has finished the 'type erasure' mechanism sets in; it doesn't do anything, it just
uses the raw type where you had specified a generic type.
This is how you define a List that stores Strings:

List<String> list= new ArrayList<String>();
 

You can use that 'list' to store and remove Strings in/from it and the compiler will
keep its mouth shut. If you want to store a different type in your list the compiler
will heavily complain to you.

kind regards,

Jos

[BigDaddyLH]

Here are two tutorials you may find useful:

Collections tutorial (using generics)

Generics tutorial

[JosAH]

Also have a look at this Wikipedia page. It has some fine external references.

kind regards,

Jos