You cannot access child object members via parent directly. Here, Object class is in the root or parent and Cat, Dog comes under it.

So, there are a couple of approaches on how you can achieve your use case.

Object Casting: Straightforward approach. Cast your parent to your desired child instance and then you access child object's members. Ex:

public void display (Object obj){
    if (obj instanceof Cat) {
      Cat c = obj(Cat);   // cast to child
      // do your operation on the cat object here 
   }
 if (obj instanceof Dog) {
      Dog d = obj(Dog);   // cast to child
      // do your operation on the dog object here 
   }
}

But this approach makes your code cluttered as the number of types increase. This is not the recommended approach anyway.

Interfaces: Write a top level interface which has a method display() and then, Dog and Cat class implements this interface. Now you can perform the display operation under each instance. Ex:

interface DisplayInterface {
    public void display();
}

class Dog implements DisplayInterface {
    public void display() {
        // your logic here
    }
}

class Cat implements DisplayInterface {
    public void display() {
        // your logic here
    }
}

//Inside the main method
Dog d = new Dog();
d.display();

Cat c = new Cat();
c.display();

In this method, you would not require util class to perform the display operation(and you shouldn't do it either).

Apart from above two, there are a couple of different approaches through Reflection and Generics which I don't feel the need for this use-case.

Cheers!