ClassCastException When converting Collection to array

Question

For a project of mine i'm trying to convert a given Collection to an array

I currently have this:

public class InsertionSorter< T extends Comparable<T>> {
    private T[] array;

    @SuppressWarnings("unchecked")
    public InsertionSorter(){
        array = (T[]) new Object[0];
    }
}

This gives me the following error:

java.lang.ClassCastException: java.base/[Ljava.lang.Object; cannot be cast to java.base/[Ljava.lang.Comparable;

Is there a solution for this?

And after i converted it to an array i want to to sort it and return it back as an collection. I do this as following:

collection.clear();
collection.addAll(Arrays.asList(sort(array)));
return collection;

The sort method is a method which sorts an array and returns an array of type T.

What do you want to achieve? Do you understand that Object is not same as array? Why not Object array instead of T? — SMA, Apr 15 '18 at 10:54
In essential i want to convert a Collection of type T to an array of type T — Kevin Tabak, Apr 15 '18 at 10:56
Use object array in that case... T is just provides compile type safety and not runtime... — SMA, Apr 15 '18 at 10:57
@SMA, Object array won't do. you will not be able to invoke `compareTo()` on items in the array — Sharon Ben Asher, Apr 15 '18 at 10:58
Oh sorry for not being specific. After i changed it to an array i want to return it again as a collection after i sorted the array. Im gonna edit the post a little bit. — Kevin Tabak, Apr 15 '18 at 11:01

score 0 · Answer 1 · answered Apr 15 '18 at 10:57

0

Your typedefinition T claims that instances will be at least Comparable, but then you try to assign an array of Object, which is not Comparable, thus resulting in a ClassCastException.

answered Apr 15 '18 at 10:57

M. le Rutte

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this may provide an answer as to why the exception occurs but no solution – Sharon Ben Asher Apr 15 '18 at 11:00

ClassCastException When converting Collection to array

1 Answers1