Demo :: java cast type

CalculateSize.java

public class CalculateSize<T> {
    public int sizeOf(Iterable<T> items) {
        int size = 0;
        if (items instanceof Collection) {
            size = Collection.class.cast(items).size();
        } else {
            for (Object item : items) {
                size++;
            }
        }
        return size;
    }
}

CalculateSize2.java

public class CalculateSize<T> {
    public int sizeOf(Iterable<T> items) {
        int size = 0;
        for (Object item : items) {
            size++;
        }
        return size;
    }

    public int sizeOf(Collection<T> items) {
        return items.size();
    }
}