Command pattern: Iterating over list of objects

[Daena Buyasta]

Afraid I've got lots of questions today. Following on from here here.

I'm using a LinkedList (correct choice?) to store a queue of instructions for my robot. The instructions are represented as objects like;

abstract class RobotInstruction {
    abstract public void perform(Aesma R);
}
 
class MoveForward extends RobotInstruction {
    public void perform(Aesma R) {
        R.ahead(100);
    }
}
 
class TurnLeft extends RobotInstruction {
    public void perform(Aesma R) {
        R.turnLeft(90);
    }
}

These get loaded into the LinkedList with the add method then I'm trying to read them out of the queue in the robots main run method like;

public class Aesma extends AdvancedRobot {
 
    public LinkedList IQueue;
 
    function run() {
 
        Iterator It = this.IQueue.listIterator();
        while ( It.hasNext() ) {
            RobotInstruction Ri = It.next();
            Ri.perform(this);
        }
 
    }
}

That results in a complain about "incompatible types" on this line "RobotInstruction Ri = It.next();".

How do you deal with this one? The examples I've found via Google so far have all involved casting the object returned from the Iterator to a String.

Many thanks again.
[ August 20, 2004: Message edited by: Daena Buyasta ]

[Adrian Yan]

iterator returns Object when you call it.next(). You need to cast this into the appropriate class. In your case, casting it to

RobotInstruction Ri = (RobotInstruction)It.next();

should work fine.

[Daena Buyasta]

Perfect. Many thanks!

Have to say think RoboCode is a brilliant idea - this is the first I'm I've ever felt really motivated to do stuff with Java.

[JulianInactive KennedyInactive]

I believe LinkedList is usually the best Collection to use for a queue. Jakarta Commons Collections offers a Queue class, amongst others, if you want a closer fit.

Jules