Java [unchecked] unchecked case warning

Question

Ok, I've been looking around and done alot of google searching, but I still can't find a way to avoid this warning.

Integer result = chooser.showOpenDialog(null);
if (result.equals(0))
{
    String tempHolder = chooser.getSelectedFile().getPath();
    filenameLoad = new File(tempHolder);
    filenameSave = filenameLoad;
    FileInputStream fis = null;
    ObjectInputStream in = null;
    try
    {
        fis = new FileInputStream(filenameLoad);
        in = new ObjectInputStream(fis);;
    }
    catch(IOException ex)
    {
        ex.printStackTrace();
    }

    try
    {
        loadFile = (ArrayList<Dot>)in.readObject();
    }
    catch(IOException ex)
    {
        System.out.println("Cast fail");
    }
    catch(ClassNotFoundException ex)
    {
        System.out.println("Cast fail");
    }
    catch (ClassCastException ex)
    {
        System.out.println("Cast fail");
    }

    try
    {
        in.close();
    }
    catch(Exception ex)
    {
        System.out.println("failed to close in");
    }
    save.setEnabled(true);
      gpanel.setDotList(loadFile);
  }

It gives me the warning at the line loadFile = (ArrayList)in.readObject(); I've added in the catchs so i'm not sure why it still says its uncatched. Any help? thanks?

What's the declaration of loadFile and what is text of the warning? — Ted Hopp, Apr 12 '11 at 07:08

score 10 · Accepted Answer · answered Apr 12 '11 at 07:07

It is not "uncatched", but "unchecked". The JVM cannot tell at runtime, i.e. when the cast is done, whether the ArrayList really contains Dot elements.

This warning occurs whenever you cast from a raw type to a generic type. If you are sure the cast is ok, you can suppress the warning with annotation

@SuppressWarnings("unchecked")

For this, it is good to encapsulate the cast in a small, separate method.

score 2 · Answer 2 · answered Apr 12 '11 at 07:10

2

You are not checking whether the object returned by

in.readObject();

is really an

ArrayList<Dot>

Use

ArrayList<Dot> dotList = null;
Object obj = in.readObject();
if (obj instanceof ArrayList<Dot>)
{
dotList = (ArrayList<Dot>) obj;
}

answered Apr 12 '11 at 07:10

Buurman

1,914
17
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2

Eclipse says: Cannot perform instanceof check against parameterized type ArrayList. Use the form ArrayList> instead since further generic type information will be erased at runtime. – cdunn2001 Feb 10 '12 at 22:04

Roland Illig · Answer 3 · 2011-04-12T07:18:05.613

1

It doesn't say uncatched (which correctly is spelled uncaught), but unchecked. You cannot avoid this warning when casting to a generic type, you can only suppress it. Or you can work around it:

@SuppressWarnings("unchecked")
public static <T> T castToAnything(Object obj) {
  return (T) obj;
}

With this method you can write:

loadFile = castToAnything(in.readObject());

edited Apr 12 '11 at 07:18

answered Apr 12 '11 at 07:09

Roland Illig

40,703
10
88
121

Hey thanks, I used this in my program doesn't give me that warning any more, thanks a bunch! – convergedtarkus Apr 13 '11 at 01:13

score 0 · Answer 4 · answered Apr 12 '11 at 07:07

0

It means the compiler cannot check that the object you read in, matches the type you are casting it to. Thus the unchecked warning.

BTW: You might want to work on your error handling to make it simpler and clearer. ;)

answered Apr 12 '11 at 07:07

Peter Lawrey

525,659
79
751
1,130

Yea, I just learned about exceptions like 4 days ago, so when I got that warning I though it meant I needed to catch an exception, so I just hit it with everything. – convergedtarkus Apr 13 '11 at 01:14
@marblecatdog, Sounds fine for now. You might find that haven't a small number of catches around all the code is better. – Peter Lawrey Apr 13 '11 at 08:31

score 0 · Answer 5 · answered Apr 12 '11 at 07:08

0

What you see is a compiler warning that you are trying to convert an Object into a ArrayList<Dot> without first checking if the Object actually contains a List of Dot and not e.g. a List of Foo.

answered Apr 12 '11 at 07:08

Heiko Rupp

30,426
13
82
119

Java [unchecked] unchecked case warning

5 Answers5

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