How can I get the class object from its member variable?

Question

I'm currently working on this code, I want to pass an ID to a member function to get the object.

public class Car {

   private int _ID;
   private String name;
   private String model;

   Car(int _id, String name, String model){
       this._ID = _id;
       this.name = name;
       this.model = model;
   }

   ....

   public static Car getCar(int _id){
       Car mCar;
       //TODO: Algo to get car
       return mCar;
   }

}

Is there any way I can get the object in this way?

Any help is appreciated! Thank You!

Answer 1

You'll need to keep a Map of objects by key. Here's one way to do it:

public class Car {

   private int _ID;
   private String name;
   private String model;

   Car(int _id, String name, String model){
       this._ID = _id;
       this.name = name;
       this.model = model;
       carsById.put(_id, this);  // <-- add to map
   }

   ....

   private static Map<Integer, Car> carsById = new HashMap<>();

   public static Car getCar(int _id){
       return carsById.get(_id);
   }

}

Answer 2

There's no predefined way to do that. You'd have to have Car or something else maintain a Map<Integer,Car> or similar of cars. This would usually be best done not in Car itself, but in the code using it.

Answer 3

Unless you have a list (or map or tree or anything else suitable) of created Car , it's not possible with your current code only. A good practice is to separate this list out of Car class, maintained elsewhere. But if you insist, shmosel provides one way.