Error: cannot resolve symbol

[fundean]

This error occurs in the following code:

public class example {

public static void main(String[] args) {

ArrayList list = new ArrayList();

for (int i = 0; i < 4; i++)
{
list.add (new Integer (i*i));
System.out.println (list.get(i));
}

}
}

Does anyone have any suggestions how to print the elements in the arraylist? The error I get is

"cannot resolve symbol class ArrayList"

TIA

[Dillinger4]

Try adding in an import directive. import java.util.*;

[Dillinger4]

This code uses java 5's(jdk1.5.0) new feature called generics. They are supposed to increase type safety by only allowing the <type> or it's subtypes to be stored within the Collection. Also casting should not be needed when grabbing an element out of a collection to be stored in ref variable of the <type>. But for some reason a cast is still needed ie. Integer integer = (Integer)i.next(); even though the Collection is specified only to hold <Integer> types. If <type> is added to the Iterator then the cast is not needed.

 for(Iterator<Integer> i = list.iterator();i.hasNext();){
   Integer integer = i.next();  then the cast is not needed.   
 }

   import java.util.*; 

   List<Integer> list = new ArrayList<Integer>();
    int element = 0; 

   while(true){
     list.add(new Integer(element)); 
     element = element + 1; // add 4 elements 
     if(element == 4) break; 
   }

    for(Iterator i = list.iterator();i.hasNext();){
      Integer integer = (Integer)i.next();  
      System.out.println(integer); 
   }

[CornedBee]

But for some reason a cast is still needed ie. Integer integer = (Integer)i.next(); even though the Collection is specified only to hold <Integer> types.

The Iterator doesn't know where it came from. That's the weird thing about Java's generics. If the iterator itself doesn't have the type specified, then it's just a normal iterator over Objects.

[Dillinger4]

Posted by CornedBee

The Iterator doesn't know where it came from. That's the weird thing about Java's generics. If the iterator itself doesn't have the type specified, then it's just a normal iterator over Objects.

Yeah it's kinda odd how the language dosen't force the deveopler to specify a type when declaring an Iterator, but then again i guess it's not needed. I don't really see any added benefit of type saftey by having to do that.

[CornedBee]

The problem is that the system cannot determine what type it's supposed to be. An Iterator is just an Iterator. An Iterator<Byte> is what does the type checking.