CODEWITHSUNDEEP
javareflection
Gherbi Hicham
Gherbi Hicham

Reputation: 2594

How to get the the object from its instance field java?

Let's say I have two classes Animal and Food:

   public class Animal {
        String animalName = "";
        Food animalFood;
        public Animal(String animalName, Food food) {
            this.animalFood = animalFood;
            this.animalName = animalName;
        }
    }

    public class Food {
        String foodType;
        String foodName;
        public Food(String foodType, String foodName) {
            this.foodName = foodName;
            this.foodType = foodType;
        }
    }

    public static void main(String[] args) {
        Food dogFood = new Food("meat", "beef");
        Animal animal = new Animal("Max", dogFood);
        //problem: get animal from dogfood
    }

Is there anyway, through Reflection or otherwise to get an instance of a class from its fields (assuming that you have access to the fields)? Edit: The example obviously isn't the real problem, so lets say I only have the dogfood instance which is created from an anynomous Instance of Animal (animal in this case) how do I get animal from it?

Upvotes: 0

Views: 374

Answers (1)

Chris Thompson
Chris Thompson

Reputation: 35598

I think what you're trying to do is this:

Given 

public class Animal {
        String animalName = "";
        Food animalFood;
        public Animal(String animalName, Food food) {
            this.animalFood = animalFood;
            this.animalName = animalName;
        }
    }

And then something like 

public static void main(String[] args) {
        Food dogFood = new Food("meat", "beef");
        doSomethingWithAnimal(new Animal("Max", dogFood)); // <-- anonymous creation of an Animal
        //problem: get animal from dogfood
        Animal theAnonymousAnimal = //get it via reflection from dogFood
    }

No, this isn't possible. Food does not contain a reference to Animal therefore you cannot. If Food had an Animal field and in the Animal constructor you set that reference, then yes, you could via normal reflection.

Upvotes: 1

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