Is it possible to create
ArrayList<Object type car,Object type bus> list = new ArrayList<Object type car,Object type bus>();
I mean add objects from different classes to one arraylist?
Thanks.
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5 Answers
Yes, it's possible:
public interface IVehicle { /* declare all common methods here */ }
public class Car implements IVehicle { /* ... */ }
public class Bus implements IVehicle { /* ... */ }
List<IVehicle> vehicles = new ArrayList<IVehicle>();
The vehicles list will accept any object that implements IVehicle.
Comments
Yes you can. But you need a common class to your object types. In your case this would be Vehicle.
So for instance:
Vehicle class:
public abstract class Vehicle {
protected String name;
}
Bus class:
public class Bus extends Vehicle {
public Bus(String name) {
this.name=name;
}
}
Car class:
public class Car extends Vehicle {
public Car(String name) {
this.name=name;
}
}
Main class:
public class Main {
public static void main(String[] args) {
Car car = new Car("BMW");
Bus bus = new Bus("MAN");
ArrayList<Vehicle> list = new ArrayList<Vehicle>();
list.add(car);
list.add(bus);
}
}
9 Comments
Serv0
ok, what about when i read the lines from the file i don't know what object i read. I have the array of strings and i need to assign it to a correct object based on the attributes from file.?
Nejc
This can not be directly solved with this implementation. You can have a function in
Vehicle class called createVehicle, which will try to parse the input string, and create an appropriate object. For instance, the function could look-up which is the manufacturer of the vehicle - if it is BMW, then this is a Car, in other case it is a Bus.Serv0
Is this correct? the second array value is the objectType so i do this. 'ArrayList<Car> items = new ArrayList<Car>(); while ((strLine = br.readLine()) != null) { String s[] = strLine.split("\\|"); if(s[2].equals("Audi")){ Audi myAud = new Audi(s[0], s[1], s[2], s[4]); items.add(myAud); } else if(s[2].equals("BMW")){ BMW myBmw = new BMW(s[0], s[1], s[2], s[3], s[4]); items.add(myBmw); } else if(s[2].equals("Opel")){ Opel myOpe = new Opel(s[0], s[1], s[2], s[3], s[4]); items.add(myOpe); } else if(s[2].equals("Mazda")){ Mazda myMaz = new Mazda(s[0], s[1], s[2], s[3]); items.add(myMaz); } }'
Nejc
Yeah, something in those lines. But here you need to sub-class all car manufacturers, which would take a lot of time, and also it is not modular. So I would stick with the representation, where you have class
Car. And then while constructing an object, you would call new Car(s[0],s[1],s[2],s[3],s[4]), where s[2] is obviously the car brand.Nejc
For that, see stackoverflow.com/questions/2784514/… . You need to implement custom
Comparator. |
Get use of polymorphism. Let's say you have a parent class Vehicle for Bus and Car.
ArrayList<Vehicle> list = new ArrayList<Vehicle>();
You can add objects of types Bus, Car or Vehicle to this list since Bus IS-A Vehicle, Car IS-A Vehicle and Vehicle IS-A Vehicle.
Retrieving an object from the list and operating based on its type:
Object obj = list.get(3);
if(obj instanceof Bus)
{
Bus bus = (Bus) obj;
bus.busMethod();
}
else if(obj instanceof Car)
{
Car car = (Car) obj;
car.carMethod();
}
else
{
Vehicle vehicle = (Vehicle) obj;
vehicle.vehicleMethod();
}
2 Comments
Serv0
that is exactly what am i doing now but how can i acces the methods from extended classes?
Serv0
Is this correct? the second array value is the objectType so i do this. 'ArrayList<Car> items = new ArrayList<Car>(); while ((strLine = br.readLine()) != null) { String s[] = strLine.split("\\|"); if(s[2].equals("Audi")){ Audi myAud = new Audi(s[0], s[1], s[2], s[4]); items.add(myAud); } else if(s[2].equals("BMW")){ BMW myBmw = new BMW(s[0], s[1], s[2], s[3], s[4]); items.add(myBmw); } else if(s[2].equals("Opel")){ Opel myOpe = new Opel(s[0], s[1], s[2], s[3], s[4]); items.add(myOpe); } else if(s[2].equals("Mazda")){ Mazda myMaz = new Mazda(s[0], s[1], s[2], s[3]); items.add(myMaz); } }'
You can't specify more than one type parameter unfortunately, so you'll have to find a common superclass for your types and use that. An extreme case would be just using Object:
List<Object> list = new ArrayList<Object>();
Be careful that you will need to cast the result to the specific type that you need if you retrieve an item (to get full functionality, not just the common one):
Car c = (Car)list.get(0);
1 Comment
Serv0
Thanks, but in my case i cannot use this solution because i read the attributes from the array and i don't know what object i get from file.
Create a class and use polymorphism. And then to pick up the object in the click, use instanceof.
