Casting to an List<Serializable>

[Whatty]

Good afternoon,

I am trying to return a List<Serializable> from a method

    public List<Serializable> getDBInfo() {
        return ApplicationConfiguration.getInstance().getDbDescriptors();
    }

where the method getDbDescriptors is:

    public List<DBDescriptor> getDbDescriptors() {
        return this.dbDescriptors;
    }

but it is complaining about

Multiple markers at this line
	- Type mismatch: cannot convert from List<DBDescriptor> to 
	 List<Serializable>
	- Cannot cast from List<DBDescriptor> to List<Serializable>

so I figured I would just cast it to the type expected:

        return (List<Serializable>)(ApplicationConfiguration.getInstance().getDbDescriptors());

but it does not like that either.

Am I missing something obvious here or is this not possible.

I could of course just iterate and create a new list but really don't want to create a new object unless I absolutely have too.

Thanks in advance.

Whatty

[Fubarable]

I'm no pro at generics, far from it, but what about doing,...

    public List<? extends Serializable> getDBInfo() {
        return ApplicationConfiguration.getInstance().getDbDescriptors();
    }

[r035198x]

The error message is very explicit. Those two are not the same. Why did you expect it to work?

[Whatty]

I just read the following whitepaper on Generics and wow!

Generics Tutorial (Generics in the Java Programming Language) - http: //java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf

However, your suggestion worked, as example:

    public List<? extends Serializable> getSerializedDBInfo() {
        return ApplicationConfiguration.getInstance().getDbDescriptors();
    }
    
    @SuppressWarnings("unchecked")
    public void serializedDBTest() {
        List<Serializable> results = (List<Serializable>)this.getSerializedDBInfo();
        for (Serializable serial : results) {
            // do something
        }
    }

to R035198x - yes, you are correct, it is very explicit (thanks I was unaware of that) but already tried to cast it.

Help instead of flaming someone is a much better approach but that IMHO.

Whatty

[r035198x]

I wonder what gave you the idea that I was trying to flame.
You never mentioned that DBDescriptor is in fact Serializable so it seemed strange to me that you would want to substitute one for the other.
The good thing is that at least you read the generics tutorial. It's usually pointless to try to use a feature without first reading a relevant tutorial about that feature.

P.S ignoreList++;

[Whatty]

Sorry I assumed that it was obvious that DBDescriptor was in fact Serializable, and the reason I mentioned the quote-unquote flame; was that your post did not offer any real help.

Thanks for the assistance nonetheless