👀 Views: 192 💬 Answers: 1 📅 Created: 2025-06-06

java generics streams classcastexception

Quick question that's been bugging me - I'm working with a `ClassCastException` while trying to process a list of objects using Java Streams and generics. Here’s the scenario: I have a base class `Animal` and two subclasses `Dog` and `Cat`. I'm trying to filter a list of `Animal` objects and cast them to their respective types. My code looks something like this: ```java import java.util.ArrayList; import java.util.List; import java.util.stream.Collectors; class Animal { String name; Animal(String name) { this.name = name; } } class Dog extends Animal { Dog(String name) { super(name); } } class Cat extends Animal { Cat(String name) { super(name); } } public class AnimalFilter { public static void main(String[] args) { List<Animal> animals = new ArrayList<>(); animals.add(new Dog("Rex")); animals.add(new Cat("Whiskers")); List<Dog> dogs = animals.stream() .filter(animal -> animal instanceof Dog) .map(animal -> (Dog) animal) .collect(Collectors.toList()); } } ``` When I run this, I get a `ClassCastException` indicating that a `Cat` is being cast to a `Dog`. I've double-checked that the filter is correctly checking the instance type before the cast. I think the scenario might be related to how the stream processes elements, but I’m not sure. I've looked at the documentation for the `stream()` method and the behavior of `instanceof`, but this question continues. I'm using Java 11, and I’ve also tried using `peek()` to debug the stream processing, which shows that the filtering seems to be correct. Any insights on what might be going wrong would be greatly appreciated. Is there something I’m missing about how generics and streams work in this context?