java ArrayList contains different objects

Answer 1

Create a class and use polymorphism. And then to pick up the object in the click, use instanceof.

Answer 2

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();
}

Answer 3

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); 

Answer 4

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.

Answer 5

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);
   }
}