How count the value of array？

Sorry, i need to clarify detailly.

I'm using Java to write simple array recording 3 times stock buying; every new car initiated is presented as new transaction made:

~~ 1 share purchased at time $100/share.

2 shares are purchased at time $200/share.

3 shares are purchased at time $300/share.

Total 6 shares in hand. ~~

How to calculate the average buying price per share ? Which continually run by keep adding new car.

package javaex;

import java.util.ArrayList;
import java.util.function.Predicate;

    public class javaExstockprice
        public static void main(String[] args){
         ArrayList<Car> al= new ArrayList();
        al.add(new Car(1,100));
        al.add(new Car(2,200));
        al.add(new Car(3,300));

        System.out.println("showsharesbuyingmethod-alltransaction = shares : buying");
        al.forEach(c->c.showsharesbuying() );
        System.out.println();
        al.removeIf(c->c.shares>1);
        System.out.print("transcation amount 1 share / below");
        System.out.println();
         al.forEach(c->c.showsharesbuying() );
        System.out.println();
    }







    class Car
    float shares;
    float buying;
    Car (float a, float b) {
        shares = a;
        buying = b;
    }

    void showsharesbuying() {
        System.out.println("showsharesbuying " + shares+ " : " + buying);
    }

Well, trying to guess what you want, here is what comes to my mind:

import java.util.List;
import java.util.ArrayList;
import java.util.function.Predicate;

public class JavaExStockPrice {

    public static void main(String[] args){

        List<Car> al= new ArrayList();
        al.add(new Car(1,100));
        al.add(new Car(2,200));
        al.add(new Car(3,300));

        System.out.println("showsharesbuyingmethod-alltransaction = shares : buying");
        al.forEach(c->c.showSharesBuying() );
        System.out.println("Avg: " + priceAvg(al));
        System.out.println();
        al.removeIf(c->c.shares>1);
        System.out.print("transcation amount 1 share / below");
        System.out.println();
        al.forEach(c->c.showSharesBuying() );
        System.out.println("Avg: " + priceAvg(al));
        System.out.println();
    }

    static double priceAvg(List<Car> l) {
        return l.stream().mapToDouble(c -> c.buying * c.shares).average().getAsDouble() / 
                    l.stream().mapToDouble(c -> c.shares).average().getAsDouble();
    }

}



class Car {
    float shares;
    float buying;

    Car (float a, float b) {
        shares = a;
        buying = b;
    }

    void showSharesBuying() {
        System.out.println("showsharesbuying " + shares+ " : " + buying);
    }
}

Having logic on static methods like this is not a good idea, but I'm not sure if that's what you want to know.