Chapter First Design Templates: Decorator Behavior

Question

This is a question about the behavior of the code, not the template itself. I will lay out the code below

  public abstract class Beverage {
    protected String description;

    public String getDescription(){
        return description;
    }
    public abstract BigDecimal cost();
}


public abstract class CondimentDecorator extends Beverage{
    @Override
    public abstract String getDescription();
}

public class HouseBlend extends Beverage{

    public HouseBlend() {
        description = "House Blend";
    }

    @Override
    public BigDecimal cost() {
        return BigDecimal.valueOf(.89);
    }

}

public class Mocha extends CondimentDecorator{
    Beverage beverage;

    public Mocha(Beverage beverage) {
        this.beverage = beverage;
    }

    @Override
    public String getDescription() {
        System.out.println("desc: " + beverage.getDescription());
        return beverage.getDescription() + ", Mocha";
    }

    @Override
    public BigDecimal cost() {
        System.out.println("bev: "+beverage.cost());
        return BigDecimal.valueOf(.20).add(beverage.cost());
    }

}

public class CoffeeTest {
        public static void main(String args[]){
            Beverage blend = new HouseBlend();
            blend = new Mocha(blend);
            blend = new Mocha(blend);
            blend = new Mocha(blend);
            System.out.println(blend.getDescription() + " * "+blend.cost());
        }
}

When CoffeeTest is running, I get the following output, which I would like to understand

1    desc: House Blend
2    desc: House Blend, Mocha
3    desc: House Blend
4    desc: House Blend, Mocha, Mocha
5    desc: House Blend
6    desc: House Blend, Mocha
7    desc: House Blend
8    bev: 0.89
9    bev: 1.09
10    bev: 0.89
11    bev: 1.29
12    bev: 0.89
13    bev: 1.09
14    bev: 0.89
15    House Blend, Mocha, Mocha, Mocha * 1.49

So these are my questions:

• I expected "desc" and "bev" to be printed 3 times, so why xtra lines?
• How is "House Blend, Mocha, Mocha" printed in the absence of an explicit state?
• I have the same question about the "cost" of how beverage.cost()to maintain a fortune by adding amounts.

I am sure that the answers lie in the polymorphism between Beverage and CondimentDecorator.

Answer 1

"House Blend, Mocha, Mocha", ?

3 . a, b c. , :

Beverage a = new HouseBlend();
Beverage b = new Mocha(a);
Beverage c = new Mocha(b);
System.out.println(c.getDescription() + " * "+c.cost());

, , , .

blend = new Mocha(blend);

, .

blend.getDescription() , c, getDescription b, getDescription a. getDescription() a "House Blend". , getDescription() b "House Blend, Mocha". getDescription() c "House Blend, Mocha, Mocha".

getCost().

Answer 2

Mocha.getDescription System.out.println addiotionally -, main void. :
desc: Blend
desc: ,
desc: Blend
bev: 0,89
bev: 1.09
bev: 0,89
, , * 1.29
void main Mocha,

public static void main(String[] args) {
        Beverage blend = new HouseBlend();
        blend = new Mocha(blend);
        blend = new Mocha(blend);
        blend = new Mocha(blend);
        System.out.println(blend.getDescription() + " * "+blend.cost());
}

, :
HouseBlend has_a (Mocha has_a (Mocha has_a (Mocha)))

Answer 3

In getDescription, you call beverage.getDescription () twice, both lines of print. A.