generics - map of lists

[Sharon whipple]

Hi all

On the following code
Compiler is giving this warning (line 1):
List is a raw type. References to generic type List<E> should be parameterized

1> HashMap<String,List> levelsMap = new HashMap<String,List>();
 
2> List<String> levels = new ArrayList<String>();
3> levels.add("bla bla");
...
 
4> levelsMap.put("bla bla2", levels);
 
...

What is the correct way to init levelsMap ?

Thank you very much
Sharon

[Rob Spoor]

1> HashMap<String,List<String>> levelsMap = new HashMap<String,List<String>>();

After all, you don't want to insert lists, you want to insert lists of strings.

[Sharon whipple]

Thank you!
on the same matter, for this code :

List<String> lst =  query.getResultList();

The compiler gives warning for
Type safety: The expression of type List needs unchecked conversion to conform to List<String>
Why is that?

Thank you
Sharon
[ September 24, 2007: Message edited by: Sharon whipple ]

[Rob Spoor]

I can't be sure without seeing the code, but my guess is that query.getResultList() returns List, not List<String>.

You can either modify query.getResultList() to return List<String> instead, or if you can't (because it's not your code) put the following line above this one:

@SuppressWarnings("unchecked")

This will remove the warning, but it is really better to change the code of query.getResultList() instead.

For anyone who says you can cast to (List<String> ) instead of suppressing warnings, that cast will cause a warning as well
[ September 24, 2007: Message edited by: Rob Prime ]

[Huan Niu]

Modify your code to:

HashMap<String,List<String>> levelsMap = new HashMap<String,List<String>>();


It will be fine. Did that answer your question?

[Huan Niu]

At most occasions, we say:

Map<String,List<String>> levelsMap = new HashMap<String,List<String>>();


Using interface gives you more flexible, and it's the OOP way...

[Sharon whipple]

Originally posted by Huan Niu:
Modify your code to:

HashMap<String,List<String>> levelsMap = new HashMap<String,List<String>>();

It will be fine. Did that answer your question?

Yes it answered my question. thank you

About the interfaces this code is imported code from other department = anyway I will be glad to hear other implementation suggestion.

About the query.getResultList()
What I don't understand is why query.getResultList() not generify?
(Query class: javax.persistence.Query) in Javaee-5.0.jar.

[Bill Shirley]

Yes, unfortunately EJB 3.0 Persistence did not generify their collections, and the Query.getResultList() returns a List and not a List<Object>. You can't cast your way out of a compiler warning (without other settings sent to the compiler).

So (as of Nov 2007),

import javax.persistence.Query;
...
@SuppressWarnings("unchecked")
public List<MyType> getTypes() {
Query query = ...;
...
return query.getResultList();  // cast warning was here
}

This is something that EJB Persistence needs to fix.
It likely won't happen until mid 2008.
Make a note of these in your code so you can go clean them up later!