'warning: [unchecked]' wrt java.util.List getSubplots()

[RichardWest]

I am trying to extend the various combined plot classes (e.g. CombinedRangeXYPlot) to add functionality. Part of this functionality requires me to create an ArrayList containing the combined plot's subplots. When compiling with jdk-1.5.0_05 (Java 5), I am getting the following warning:

Code: Select all

warning: [unchecked] unchecked call to ArrayList(java.util.Collection<? extends E>) as a member of the raw type java.util.ArrayList
        ArrayList l_subplots = new ArrayList(getSubplots());

I know what the warning is, what it means, and how I normally address them. However, I do not know how to fix the warning in this case since getSubplots() returns a raw java.util.List. Without changing the JFreeChart source (we need to keep it backwards compilable, how can I address this warning? Before you suggest it, suppressing the warning is not an option.

[jwenting]

You can't. There are only 3 options that will get rid of those warnings:
1) genericise the code
2) add the @SuppressWarnings("unchecked") annotation
3) suppress the warning at compiler level using the -Xlint:-unchecked flag.

As you don't want to do any of the above, you'll have to live with it.

[dtopolsek]

declare, in fact define your l_subplots ArrayList as ArrayList<? extends E> l_subplost = new ArrayList<? extends E>(getSubplots()).


? helped ?

[RichardWest]

declare, in fact define your l_subplots ArrayList as ArrayList<? extends E> l_subplost = new ArrayList<? extends E>(getSubplots()).


? helped ?

Of course it does not help. E is a placeholder for either a class or interface (similar to the preverbial T in C++ templates). What you suggested would not even compile.

[RichardWest]

Code: Select all

warning: [unchecked] unchecked call to ArrayList(java.util.Collection<? extends E>) as a member of the raw type java.util.ArrayList
        ArrayList l_subplots = new ArrayList(getSubplots());

It looks like the only way to code this without the warnings is:

Code: Select all

Object[] l_subplots = getSubplots().toArray();
((<class>)l_supplots[<index>]).doSomething();

Trying to pass any type information to the toArray() method throws a warning.

[jwenting]

logical. As soon as you pass a specific type you're triggering the warning by having a typed collection to which you're adding elements with no specific type in the (1.4 compliant) code.

By telling it to use Object[] you're effectively creating an untyped collection which will fit anything.
That's the problem of mixing generics aware code with pre-generics code. Something has to give, and usually it's the implicit casts and type safety.