Q:

How to get an item in an arraylist from a diffrent class

I'm trying to get an 'point' from an arraylist that is in a different class. There is the producer that is sending a 'bid' or point. But it has to first get the point before it can send it. The logic in initalBid() is to get the thing in slot 0 when the market (another class) calls the initalBid(). There is also a producerCurve class which creates the producers personal curve through the AbstractCurve class which create a general curve. General idea: how do I get an item from inside the arraylist in my initalBid method.
Producer initalBid():
public Point initalBid()
{
    return producer.get(0);
}

Producer Curve:
public class ProducerCurve extends AbstractCurve 
{

public ProducerCurve() 
    {
        super(10, -1, 0, 1);
    }
public ProducerCurve(int np, double m, double b, int dx) 
{
    super(np,m,b,dx);
}

}

Abstract Curve:
 import java.util.ArrayList;
 public abstract class AbstractCurve {
 ArrayList<Point> myCurve = new ArrayList<Point>();

 public AbstractCurve(int np, double m, double b, int dx)
    {

     for(int i=0; i<np; i++)
     {
         int x = i*dx;
         double y = m*x+b;
         if(y<0) throw new IllegalArgumentException();
         ArrayList<Point> myCurve = new ArrayList<Point>();
         myCurve.add(new Point(x, y));
     }  
}

 public boolean contains(Point p)
    {
        for(int index=0; index< myCurve.size(); index++ )
        {
            myCurve.equals(index);  
            {
                return true;
            }
        }
        return false;
    }
}

A:

Since you need to get elements from the ArrayList, and ProducerCurve is more or less just a wrapper to initialize that ArrayList: I would probably just extend ArrayList:
import java.util.ArrayList;

public abstract class AbstractCurve extends ArrayList<Point> {

    public AbstractCurve(int np, double m, double b, int dx) {
        for (int i = 0; i < np; i++) {
            int x = i * dx;
            double y = m * x + b;
            if (y < 0) {
                throw new IllegalArgumentException();
            }
            this.add(new Point(x, y));
        }
    }
}

Then you can just use the methods on ArrayList:
public Point initalBid() {
    if (producer.size() > 0) {
        return producer.get(0);
    }
    return null;
}

For looping over your points you can use the collections APi:
public void loopOverBids() {
    for (Point thisPoint : producer) {
        System.out.println(thisPoint);
    }
}

