如何显示 Arraylist 中随机元素的方法？

Question

I know how to get a random element from ArrayList , but what I don't know is how to also display only 1 element's methods. For example, I have two subclasses with a few methods that are very basic (they basically just print some stuff), and the ArrayList is in the superclass.

This is my code with the Cat and Dog being subclasses. Now the code prints one of them but methods from both classes are displayed. If the program picks Dog for example, then I want only the results from Dog's noise() and furr() to be displayed. How could I do this?

ArrayList<Animal> an = new ArrayList<>();
        an.add(new Cat());
        an.add(new Dog());

       for (Animal a : an) { 
        a.noise();
        a.furr();
    }
   
    int randomIndex = (int) (Math.random() * an.size());
    System.out.println( "The animal: " +  an.get( randomIndex ));

Answer 1

You're looping through all animals and calling Animal#noise and Animal#furr. What you want to do instead is get the animal at the index you've selected and call those methods on that one instance.

It's also worth mentioning that it's unconventional to allow classes to have more than one responsibility. When the Animal super class maintains a List with Animal references you break this convention. Instead, use a pattern like the service locator pattern to avoid this.

int randomIndex = (int) (Math.random() * an.size());

Animal animal = an.get(randomIndex);

animal.noise();
animal.furr();

Answer 2

You can create a method for that after you select the random element pass it to a method then print it. I find it for you.

public int getRandomElement(List<Integer> list) 
{ 
    Random rand = new Random(); 
    return list.get(rand.nextInt(list.size())); 
}