Unchecked conversion

Question

Hi all,
I have a Swing application that uses few generic classes. Currently I'm trying to remove all warnings in my code (adding serialVersionUID is very annoying by the way). I want to express one of my problem with a basic sample.
Consider that I define a generic class A:
public class A<T> {
     public List<String> getList() {
          return new ArrayList<String>();
}And another class B that uses A:
public class B {
     public void doSomethingUnsecure(A a) {
          List<String> list = a.getList();
          for(String item : list) {
               System.out.println(item);
     public void doSomethingSecure(A a) {          
          for(Object o : a.getList()) {
               String item = (String)o;               
               System.out.println(item);
}I have a few question regarding this piece of code:
1) Why 'List<String> list = a.getList();' in 'doSomethingUnsecure' gives a warning ? It's not the case if A is not generic.
The warning is "Type safety: The expression of type List needs unchecked conversion to conform to List<String>"
2) Why I get no warning at all for 'doSomethingSecure' ?
3) Is there a better way to go around this problem than casting each element in the list (like in doSomethingSecure) ?

Answer 1

>
public class A<T> {
     public List<String> getList() {
          return new ArrayList<String>();
public class B {
     public void doSomethingUnsecure(A a) {
          List<String> list = a.getList();
          for(String item : list) {
               System.out.println(item);
     public void doSomethingSecure(A a) {          
          for(Object o : a.getList()) {
               String item = (String)o;               
               System.out.println(item);
}1) Why 'List<String> list = a.getList();' in 'doSomethingUnsecure' gives a warning ? It's not the case if A is not generic.Because once you declare A<T>, java is going to generate a warning every time you use A without some kind of <> after it.
A generic type is forever generic. Using the "raw" type is permissible, and sometimes even necessary, but it always gets a warning.
You want to tell it A<SomeClass>, and you want to try and make sure that your <SomeClass> is correct. If you can't, then you might be able to get away with using A<?>, as suggested, if you are treating the A<> item as read-only.
2) Why I get no warning at all for 'doSomethingSecure' ?Because anything can fit into a variable of type Object, so iterating with "Object o" is okay. No cast is needed in this case.
3) Is there a better way to go around this problem than casting each element in the list (like in doSomethingSecure) ?Get the type parameters right, as mentioned above.
=Austin