CODEWITHSUNDEEP
java
user3339562
user3339562

Reputation: 1385

Check if parent class is instance of child class

I have one class defined like this:

class Car {

}

And many other defined like this:

class Audi extends Car {

}

class Seat extends Car {

}

class Mercedes extends Car {

}

class Opel extends Car {

}

...

I have a situation where I receive a list of all these cars which is defined like this:

List<Car> cars = new ArrayList<Car>();

In that list there are many different cars so how can I find out which one is Audi, which one is Seat etc?

I've tried to do this for cars for which I know they are of type Audi:

Audi audi = (Audi) cars.get(0);

This throws ClassCastException. How to handle this situation?

Upvotes: 6

Views: 19724

Answers (4)

Dmytro
Dmytro

Reputation: 2019

You can use instanceof before casting. For example:

Car someCar = cars.get(0);
Audi audi = null;
if(someCar instanceof Audi){
audi = (Audi) someCar;
}
if(audi != null){
//...

But likely it's a bad idea, because generics was introduced to avoid using casting and instanceof.

Upvotes: 3

Peter Pei Guo
Peter Pei Guo

Reputation: 7870

Check with instanceof, for example:

car instanceof Audi

This returns true if variable car is an instance of Audi, otherwise returns false.

Upvotes: 2

Jesper
Jesper

Reputation: 207006

You can use instanceof:

Car car = cars.get(0);
if (car instanceof Audi) {
    // It's an Audi, now you can safely cast it
    Audi audi = (Audi) car;
    // ...do whatever needs to be done with the Audi
}

However, in practice you should use instanceof sparingly - it goes against object oriented programming principles. See, for example: Is This Use of the "instanceof" Operator Considered Bad Design?

Upvotes: 8

Tobias
Tobias

Reputation: 7771

Obvious or not, this will do the trick:

Car car = cars.get(0);
if(car instanceof Audi) {
  Audi audi = (Audi) car;
}

Upvotes: 3

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