Casting Object to List results in unchecked cast warning

Question

I want to cast Object to List<IAnalysisData> . The object was read in from a database. However, I am getting an annoying warning saying that the cast is unchecked.

private List<IAnalysisData> deserialize(byte[] bytes) throws IOException, ClassNotFoundException
{
    List<IAnalysisData> analysisDataList = null;
    ByteArrayInputStream in = new ByteArrayInputStream(bytes);
    ObjectInputStream oos = new ObjectInputStream(in);
    Object o = oos.readObject();

    analysisDataList = (List<IAnalysisData>) o; //warning here
    return analysisDataList;
}

What is the proper way to cast an object?

EDIT: I forgot to mention that IAnalysisData is an interface. The implementation is called AnalysisData .

Answer 1

The only way I know to fix something like this would be to add the

@SuppressWarnings("unchecked")

There's no way to prove what you're doing is safe really, even if you absolutely 'know' that it is.

So it would look like

@SuppressWarnings("unchecked")
private List<IAnalysisData> deserialize(byte[] bytes) throws IOException, ClassNotFoundException
{
    List<IAnalysisData> analysisDataList = null;
    ByteArrayInputStream in = new ByteArrayInputStream(bytes);
    ObjectInputStream oos = new ObjectInputStream(in);
    Object o = oos.readObject();

    analysisDataList = (List<IAnalysisData>) o; //warning here
    return analysisDataList;
}

You'll get no unchecked warning in that method after that.

Answer 2

It is not possible to check a cast to a generic type. You could use instanceof to confirm that Object o really is a List<?> but you cannot confirm that it is a List<IAnalysisData> . For safety, you could use a try/catch block to catch a ClassCastException , but that will still not hide the IDE warning. Like Andrew said, putting the @SuppressWarnings("unchecked") above the method will hide the warning for this method alone, but IDE warnings mean next to nothing in the long run.

Answer 3

Your casting syntax is fine.

You ought to check that analysisDataList is not null , which indicates casting success. That's what your IDE is telling you.

Encode this in a separate function if you use it in more than one place.