[PinguTrace]

I am trying to get information from a text file and store it back in an arrayList<String> then return this out of the method.

 ArrayList<String> back = new ArrayList<String>(); 

FileInputSteam a = new FileInputStream(filename);
ObjectInputStream b = new ObjectInputStream(a);

back = (ArrayList<String>) b.readObject();

a.close();

return back;

but I get the error warning [unchecked] unchecked cast
required ArrayList<String>
found Object


on line 6.

What am I doing wrong?

[CasiOo]

It is only a warning. But you should check the type of the object you have just read before assigning it to back. Sadly I don't believe you can check on generic types by using instanceof, you can only check if it is an ArrayList.

[Sinned]

This is a bit a strange error, because other casts works fine.
But I think the problem lies partly in the compiler and partly in the running.

Compiler warnings can always be ignored, errors can't. But this is a warning, so add this to the top of you function:

@SuppressWarnings("unchecked")

This handles the compiler part.

To solve the runtime part - I mean you don't want to let your program crash while running because it is not an ArrayList - use the following:

Object o = b.readObject();
if(o instanceof ArrayList)
	back = (ArrayList<String>) o;

This makes sure the Object is an ArrayList. (You can't check the type of the ArrayList)

I hope this helped you,

Sinned

[PinguTrace]

thankyou so much, the suppress warnings seemed to work. so thank you

[CasiOo]

PinguTrace, on 03 April 2012 - 03:26 PM, said:

thankyou so much, the suppress warnings seemed to work. so thank you

dont just suppress it without any checks :S