Generics Question

[Chandana Garlapati]

   
import java.util.*; 
class Test { 
	public static void main(String [] args) { 
		List vals = new LinkedList<String>(); // why this compiles with warning?? It is generic instant but why???
		vals.add("one"); 
		vals.add(1); 
		vals.add("two"); 
		System.out.println(vals); 
	} 
} 
 

This question is from javabeat
could anyone explain??

[Andriy Pererva]

The warning is because raw List reference is referenced to parametrized LinkedList.
LinkedList parametrization means that you have an intent to explcitly restrict collection items to String type, but the raw reference spoils all the generic effort and allows to add any object (like Integer on line 7), despite of LinkedList parametrization

[Chandana Garlapati]

But the rule is:

Non Generic ref. type + Generic instant --> compiles w/o warning
Generic ref.type + Non Generic instant --> compiles with warning

[Ankit Garg]

List vals = new LinkedList<String>();

This line of code does not generate any compiler warning. How did you compile your code?? Did you use any IDE??

[Chandana Garlapati]

Ankit Garg wrote:

List vals = new LinkedList<String>();

This line of code does not generate any compiler warning. How did you compile your code?? Did you use any IDE??

No i am trying in notepad and command prompt.

[Leonardo Carreira]

Hi Chandana..

i think you need to use Netbeans or other Java IDE..
it could help us to know the warning..

[Dragos Nica]

Chandana Garlapati wrote:

Ankit Garg wrote:

List vals = new LinkedList<String>();

This line of code does not generate any compiler warning. How did you compile your code?? Did you use any IDE??

No i am trying in notepad and command prompt.

The warning will occur only if you are trying to add something.
Every time when you try to add something to a non parameterized collection , the warning will occur. As such a list can accept any type of object, this is the compiler's way to tell you that you must pay attention to what you are adding to the list.