source: src/main/java/bargainingchips/Stack.java@ 341

package bargainingchips;

/**
 * Stack contains a number of {@link Chip} objects of the same color and price. 
 * A stack=(chip, quantity, price). 
 * Aggregation of a two stacks of the same colors, creates another stack with the total quantity but its chip in a new price equal to weighted average of the both unit prices.  
 * Aggregation of a stack with the empty stack is itself. 
 * 
 *  Immutable.
 */
public class Stack 
{
        private final Chip chip;
        private final double price;
        private final int quantity;

        public Stack(Chip c, double p, int q)
        {
                chip = c;
                price = ( (p>0) ? p : 0.0);
                quantity = ( (q>0) ? q : 0);
        }
        
        public Stack(String c, double p, int q)
        {
                this(new Chip(c), p, q);
        }
        
        /**
         * @return the chip
         */
        public Chip getChip() {
                return chip;
        }

        /**
         * @return the quantity
         */
        public int getQuantity() 
        {
                return quantity;
        }

        public double getUnitPrice()
        {
                return price;
        }
        
        public double getTotalPrice()
        {
                return price * quantity;
        }

        public String getColor()
        {
                return chip.getColor();
        }
        
        public boolean hasSameColorAs(Stack s)
        {
                return getChip().equals(s.getChip());
        }
        
        public Stack aggregateWith(Stack s) 
        {
                if (s!=null && s.hasSameColorAs(this)) 
                {
                        int q = quantity + s.getQuantity();
                        double p = (getUnitPrice()*quantity+s.getUnitPrice()*s.getQuantity())/q;
                        return new Stack(getChip(), p, q);
                } else 
                        throw new IllegalStateException("\n\n[Warning] StackClass::aggregateWith(Stack). Different colors! Aggregating "+s+" into "+this+" is not possible.");
        }       

        @Override
        public String toString() 
        {
                return getQuantity()+"x"+getChip()+"($" + getUnitPrice() + ")";
        }
        
        public static void main(String[] args) 
        {
                Stack s = new Stack("Red", 9.0, 3);
                Stack t = new Stack ("Red", 4.0, 2);
                System.out.println(s + " + " + t + " = " + s.aggregateWith(t));
                System.out.println(t + " + " + s + " = " + t.aggregateWith(s));         
        }
}