How to have an object and its subclasses as a parameter of an object-CodePudding

i have a basic question but i don't know how to solve it. pls help me!

if i have a class Zoo

public class Zoo{
    private Animal animal;
    private Long age;
}

and Animal para is this:

public class Animal{
    private String name;
}

but now i have a new class is: Dog class, extends animal

public class Dog extends Node{
    private String dogClass;
}

I want to make the animal property in Zoo also accept Dog class parameters, what should I do?

Is there an elegant way to write it like List<? extends Animal> ?

CodePudding user response：

You don't need to change anything: as Dog extends Animal, it can be assign to field Zoo.animal. You can however add a method in Zoo to get animal as an instance of a specific class:

public <T extends Animal> T getAnimal(Class<T> animalClass) {
    return animalClass.cast(animal);
}

Or, if you don't want it to throw an exception if the animal is not of the specified class:

public <T extends Animal> T getAnimal(Class<T> animalClass) {
    if (!animalClass.isInstance(animal)) {
        return null;
    }
    return animalClass.cast(animal);
}

CodePudding user response：

If I'm not mistaken, to do what you're asking, all you have to do is insert constructors in the parent and child classes and associate their values in this way:

public class Animal{
    private String name;
    public Animal(String name){
    this.name = name;
    }
}

public class Dog extends Animal{
    private String dogClass;
    public Dog(){
    super(dogClass);
    }
}

Also, if you already plan to never instantiate the Animal class directly, as it is a generic object, you could make it abstract.