Question

i am facing problem with the retyping the object to integer.

I have the object Car with 2 string attributes. First attribute is ID.
I retyped ID from string to integer

ArrayList<Car> intList = new ArrayList<Car>(); // already filled with objects 

ArrayList<Integer> intList = new ArrayList<Integer>();

for(Car tempInt : items){   
intList.add(Integer.parseInt(tempInt.getID()));
}
Collections.sort(intList); // i sorted id's

Can i retype the integer back to Car object?

for (ItemObject temp : intList) { // HERE I GET THE ERROR

if(temp instanceof Car){
System.out.println("ID : "+((Car)temp).getID())
        }}

Is this possible? I need sort objects.
Thanks.
S

Answer 1

I think you are fundamentally misunderstanding which objects are which in this scenario. When you create your ArrayList<Integer> you do not magically preserve any information about which cars those integers were connected to.

I think what you want to do is sort your list of Cars by id, correct? In that case, what you want is a Comparator: http://docs.oracle.com/javase/6/docs/api/java/util/Comparator.html

Here is an example of sorting using a Comparator:

ArrayList<Car> cars = ...//Filled with cars
Comparator<Car> carSorter = new Comparator<Car>() {
  @Override
  public int compare(Car a, Car b) {
    return a.getID() - b.getID();
  }
};
Collections.sort(cars, carSorter);//After this line, cars will be in order