Rae Rae - 4 months ago 13
Java Question

Java how to handle "Unchecked cast" for Array<MyItem> from Object

In my Android project I have made an abstract AsyncTask class in which I input the URL and if needed paging information so I don't need to keep writing the HTTP stuff etc.

I've made an abstract method, onAsyncTaskResult(Object o) which must be implemented on use.
However when casting it to the appropriate object (can be of different types) the IDE gives me a warning

"Unchecked cast for java.lang.Object to java.util.ArrayList<com.company.package.subpackage.MyItem>"


Here is my code snippet of the implemention of said function

new SuperCoolAsyncTask() {
@Override
protected void onAsyncTaskResult(Object o) {
if(o instanceof ArrayList) {
//generates warning in the following line
AppConstants.scoreStatistics = (ArrayList<MyItem>)o;
}
}
}.execute(get_url_score_statistics());


How am i supposed to cast this to an
ArrayList<MyItem>
without generating a warning?

Without the
<MyItem>
declaration it throws an "Unchecked assignment"

Answer

You cannot do it without a warning. You are casting an Object to some other class, and even if the Object is an instance of ArrayList you don't know it's generic type.

Update:

if you wrote SuperCoolAsyncTask yourself, you could parametrize the class with generics:

public abstract class SuperCoolAsyncTask<ResultType> {

    protected abstract void onAsyncTaskResult(ResultType o);

}

And then, when you invoke your code:

new SuperCoolAsyncTask<ArrayList<MyItem>>() {
    @Override
    protected void onAsyncTaskResult(ArrayList<MyItem> o) {
            AppConstants.scoreStatistics = o;
    }
}.execute(get_url_score_statistics());