Beginner's Question: "*.java uses unchecked or unsafe operations"

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sunbin - 03 Oct 2006 17:01 GMT

Hi all

I have read the net and notice this problem is caused by the version of
compiler between 1.5 and 1.4.

I tried to use the follow codes to overcome the warning msg. "uses unchecked
or unsafe operations" but not able to. Please advice. Thanks.

[code]

public class XXX
{
private ArrayList <Customer> CustDB;
.....
.....
public static void main(String[] args)
{
......
......
......
FileInputStream readFile = new FileInputStream("cust.dat");
ObjectInputStream read = new ObjectInputStream(readFile);

CustDB = (ArrayList<Customer>)read.readObject();
}
}

[/code]

I tried to typecast the read object, but yet the warning still exists.
May I know where have I did wrong?

Reply to this Message

Oliver Wong - 04 Oct 2006 14:56 GMT

> Hi all
>
[quoted text clipped - 27 lines]
> I tried to typecast the read object, but yet the warning still exists.
> May I know where have I did wrong?

Specifically, change the cast to:

CustDB = (ArrayList<?>)read.readObject();

you'll probably have to add some more casts later on in your code in
addition to making this change.

In general, don't supply generic type arguments in cast expressions.

- Oliver

Reply to this Message

sunbin - 04 Oct 2006 18:49 GMT

> Specifically, change the cast to:
>
> CustDB = (ArrayList<?>)read.readObject();
>
> you'll probably have to add some more casts later on in your code in
> addition to making this change.

Thanks for the reply.

I dont quite get what you mean. I am precisely doing what your post listed

CustDB = (ArrayList<?>)read.readObject();

but the warning msg just won't get away.

> In general, don't supply generic type arguments in cast expressions.

Sorry I do not know what's generic, mind to explain?

Reply to this Message

Oliver Wong - 04 Oct 2006 19:58 GMT

>> Specifically, change the cast to:
>>
[quoted text clipped - 10 lines]
>
> but the warning msg just won't get away.

Are you sure? In your original post, you said you wrote:

CustDB = (ArrayList<Customer>)read.readObject();

But I'm telling you to write:

CustDB = (ArrayList<?>)read.readObject();

Notice that I don't pass "Customer" as a generic type argument.

>> In general, don't supply generic type arguments in cast expressions.
>
> Sorry I do not know what's generic, mind to explain?

To put it informally, generic type arguments are the stuff that appear
between the angle brackets in your code. If you don't understand how they
work, it's probably best not to use them at all (remove everything between
the angle brackets, and the angle brackets themselves), so the code would
look like:

CustDB = (ArrayList)read.readObject();

instead of

CustDB = (ArrayList<Customer>)read.readObject();

You'll get warnings about not using generics, but you should just ignore
them, since you don't know how to use generics yet.

- Oliver

Reply to this Message

Tor Iver Wilhelmsen - 04 Oct 2006 18:54 GMT

> Specifically, change the cast to:
>
> CustDB = (ArrayList<?>)read.readObject();

Or add a @SuppressWarnings("unchecked") annotation to the method.

Reply to this Message

sunbin - 04 Oct 2006 19:04 GMT

> Or add a @SuppressWarnings("unchecked") annotation to the method.

Well how do I add that to my codes... sorry i cannot understand the
@suppress thingy.

Reply to this Message

Tor Iver Wilhelmsen - 04 Oct 2006 19:40 GMT

> Well how do I add that to my codes... sorry i cannot understand the
> @suppress thingy.

Annotations is another of the new JSE 5 features, like the generics
you already use.

http://www.oracle.com/technology/pub/articles/hunter_meta.html

Reply to this Message

sunbin - 05 Oct 2006 14:07 GMT

>> Well how do I add that to my codes... sorry i cannot understand the
>> @suppress thingy.
[quoted text clipped - 3 lines]
>
> http://www.oracle.com/technology/pub/articles/hunter_meta.html

Hey thanks. I got manage to suppress the warning message.

Reply to this Message

Thomas Hawtin - 04 Oct 2006 22:17 GMT

> I tried to use the follow codes to overcome the warning msg. "uses unchecked
> or unsafe operations" but not able to. Please advice. Thanks.

> ObjectInputStream read = new ObjectInputStream(readFile);
>
> CustDB = (ArrayList<Customer>)read.readObject();

Here's an answer I prepared earlier:

http://groups.google.com/group/comp.lang.java.programmer/tree/browse_frm/thread/
3c05ddbbe4eaaba4#doc_585daaa682e4e563

Tom Hawtin

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Beginner's Question: "*.java uses unchecked or unsafe operations"

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