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POHead First Design Patterns: Decorator behavior puzzling
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copied!<p>This is a question on the behavior of the code rather then the pattern itself. I will lay out the code below</p> <pre><code> 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()); } } </code></pre> <p>When CoffeeTest is run I get the following output which I would like to understand</p> <pre><code>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 </code></pre> <p>So these are my questions:</p> <ol> <li>I expected 'desc' and 'bev' to be printed 3x, so why the xtra lines? </li> <li>How is 'House Blend, Mocha, Mocha' printed when there is no explicit state saved?</li> <li>I have the same question about 'cost', how is <code>beverage.cost()</code> saving state by adding the amounts.</li> </ol> <p>I am sure the answers lie in polymorphism between Beverage and CondimentDecorator.</p>

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