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java - Is there a way I can check if any of the objects in an ArrayList have an object of a specific class?

问题描述

Assuming I have a class hierarchy where Monkey, Chimp, and Ape classes all inherit from an Animal Class. I now have an ArrayList where some random number of monkeys/chimps/apes are stored inside. Is there a function that can check if any Monkeys exist in that arraylist? Right now I have

for (Animal animal1 : Enclosure.HABITABLE_ANIMALS)
     {
       if (animal.getClass().equals(animal1.getClass()))
          {
                    count++;
          }
     }

and if the count is greater than 0 it returns true (in this code you HABITABLE_ANIMALS is the arraylist of animals, and animal is the Monkey) surely there is a more efficient and better way of doing this

标签： java

解决方案

There is no more efficient way to do this unfortunately, since you'll need to go through the whole List anyway (time complexity: O(n))

However, there might be a more expressive way of doing it using Stream (but it adds the overhead of creating a Stream).

If expressiveness is more important than performance, I'd suggest to go for this solution

Enclosure.HABITABLE_ANIMALS
         .stream()
         .anyMatch(animal.getClass()::isInstance)

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