I want to write a function that will create a stream of random numbers:
import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;
public class fillRandom {
public static List<Integer> IntFill(){
return new Random().ints(10,0,100).boxed().collect(Collectors.toList());
}
}
And then I want to return it to my LinkedList:
public class Main {
public static void main(String[] args) throws Exception {
List linkedList = new LinkedList<Integer>();
Print printer = new printImpl();
linkedList = (LinkedList) fillRandom.IntFill();
printer.print(linkedList);
}
}
But I get an error Exception in thread "main" java.lang.ClassCastException: class java.util.ArrayList cannot be cast to class java.util.LinkedList
Is it possible to do something to make it work without collect(Collectors.toCollection(LinkedList::new))
? If I don't want to return exactly the ArrayList
from Random
.
According to the documentation of toList
, there is no guarantee on the type of list returned, and it specifically asks you to use toCollection
There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned; if more control over the returned List is required, use
toCollection(Supplier)
.
If your reason for not using toCollection
is simply to avoid using a specific implementation in intFill
, and wants to allow the caller to specify what List
they want, you can alway give the user that option with a Supplier
parameter, just like how toCollection
does.
public static <C extends Collection<Integer>> C intFill(Supplier<C> collectionSupplier){
return new Random().ints(10,0,100).boxed()
.collect(Collectors.toCollection(collectionSupplier));
}
Usage:
List<Integer> linkedList = fillRandom.intFill(LinkedList::new);
Alternatively, rather than casting, use the LinkedList
constructor to create a LinkedList
from whatever List
is returned by the toList
collector.
List<Integer> linkedList = new LinkedList<>(fillRandom.intFill());
Note that a disadvantage of this is that it will loop over the whole list again, which may not be desirable.