|
| 1 | +--- |
| 2 | +title: Servant |
| 3 | +category: Behavioral |
| 4 | +language: es |
| 5 | +tag: |
| 6 | +- Decoupling |
| 7 | +--- |
| 8 | + |
| 9 | +## Propósito |
| 10 | +Servant se utiliza para proporcionar algún comportamiento a un grupo de clases. |
| 11 | +En lugar de definir ese comportamiento en cada clase - o cuando no podemos factorizar |
| 12 | +este comportamiento en la clase padre común - se define una vez en el Servant. |
| 13 | + |
| 14 | +## Explicación |
| 15 | + |
| 16 | +Ejemplo del mundo real |
| 17 | + |
| 18 | +> El Rey, la Reina y otros miembros reales de palacio necesitan sirvientes que les den de comer, |
| 19 | +> organizar bebidas, etc. |
| 20 | +
|
| 21 | +En otras palabras |
| 22 | + |
| 23 | +> Garantiza que un objeto servidor preste determinados servicios a un grupo de clases atendidas. |
| 24 | +
|
| 25 | +Wikipedia dice |
| 26 | + |
| 27 | +> En ingeniería de software, el patrón Servant define un objeto utilizado para ofrecer alguna funcionalidad |
| 28 | +> a un grupo de clases sin definir esa funcionalidad en cada una de ellas. Un Servant es una clase |
| 29 | +> cuya instancia (o incluso sólo clase) proporciona métodos que se encargan de un servicio deseado, mientras que |
| 30 | +> los objetos para los que (o con los que) el Servant hace algo, se toman como parámetros. |
| 31 | +
|
| 32 | +**Ejemplo programático** |
| 33 | + |
| 34 | +La clase Servant puede prestar servicios a otros miembros reales de palacio. |
| 35 | + |
| 36 | +```java |
| 37 | +/** |
| 38 | + * Servant. |
| 39 | + */ |
| 40 | +public class Servant { |
| 41 | + |
| 42 | + public String name; |
| 43 | + |
| 44 | + /** |
| 45 | + * Constructor. |
| 46 | + */ |
| 47 | + public Servant(String name) { |
| 48 | + this.name = name; |
| 49 | + } |
| 50 | + |
| 51 | + public void feed(Royalty r) { |
| 52 | + r.getFed(); |
| 53 | + } |
| 54 | + |
| 55 | + public void giveWine(Royalty r) { |
| 56 | + r.getDrink(); |
| 57 | + } |
| 58 | + |
| 59 | + public void giveCompliments(Royalty r) { |
| 60 | + r.receiveCompliments(); |
| 61 | + } |
| 62 | + |
| 63 | + /** |
| 64 | + * Check if we will be hanged. |
| 65 | + */ |
| 66 | + public boolean checkIfYouWillBeHanged(List<Royalty> tableGuests) { |
| 67 | + return tableGuests.stream().allMatch(Royalty::getMood); |
| 68 | + } |
| 69 | +} |
| 70 | +``` |
| 71 | + |
| 72 | +Royalty es una interfaz. Es implementada por las clases King, y Queen para obtener servicios de servant. |
| 73 | + |
| 74 | +```java |
| 75 | +interface Royalty { |
| 76 | + |
| 77 | + void getFed(); |
| 78 | + |
| 79 | + void getDrink(); |
| 80 | + |
| 81 | + void changeMood(); |
| 82 | + |
| 83 | + void receiveCompliments(); |
| 84 | + |
| 85 | + boolean getMood(); |
| 86 | +} |
| 87 | +``` |
| 88 | +La clase King implementa la interfaz Royalty. |
| 89 | +```java |
| 90 | +public class King implements Royalty { |
| 91 | + |
| 92 | + private boolean isDrunk; |
| 93 | + private boolean isHungry = true; |
| 94 | + private boolean isHappy; |
| 95 | + private boolean complimentReceived; |
| 96 | + |
| 97 | + @Override |
| 98 | + public void getFed() { |
| 99 | + isHungry = false; |
| 100 | + } |
| 101 | + |
| 102 | + @Override |
| 103 | + public void getDrink() { |
| 104 | + isDrunk = true; |
| 105 | + } |
| 106 | + |
| 107 | + public void receiveCompliments() { |
| 108 | + complimentReceived = true; |
| 109 | + } |
| 110 | + |
| 111 | + @Override |
| 112 | + public void changeMood() { |
| 113 | + if (!isHungry && isDrunk) { |
| 114 | + isHappy = true; |
| 115 | + } |
| 116 | + if (complimentReceived) { |
| 117 | + isHappy = false; |
| 118 | + } |
| 119 | + } |
| 120 | + |
| 121 | + @Override |
| 122 | + public boolean getMood() { |
| 123 | + return isHappy; |
| 124 | + } |
| 125 | +} |
| 126 | +``` |
| 127 | +La clase Queen implementa la interfaz Royalty. |
| 128 | +```java |
| 129 | +public class Queen implements Royalty { |
| 130 | + |
| 131 | + private boolean isDrunk = true; |
| 132 | + private boolean isHungry; |
| 133 | + private boolean isHappy; |
| 134 | + private boolean isFlirty = true; |
| 135 | + private boolean complimentReceived; |
| 136 | + |
| 137 | + @Override |
| 138 | + public void getFed() { |
| 139 | + isHungry = false; |
| 140 | + } |
| 141 | + |
| 142 | + @Override |
| 143 | + public void getDrink() { |
| 144 | + isDrunk = true; |
| 145 | + } |
| 146 | + |
| 147 | + public void receiveCompliments() { |
| 148 | + complimentReceived = true; |
| 149 | + } |
| 150 | + |
| 151 | + @Override |
| 152 | + public void changeMood() { |
| 153 | + if (complimentReceived && isFlirty && isDrunk && !isHungry) { |
| 154 | + isHappy = true; |
| 155 | + } |
| 156 | + } |
| 157 | + |
| 158 | + @Override |
| 159 | + public boolean getMood() { |
| 160 | + return isHappy; |
| 161 | + } |
| 162 | + |
| 163 | + public void setFlirtiness(boolean f) { |
| 164 | + this.isFlirty = f; |
| 165 | + } |
| 166 | + |
| 167 | +} |
| 168 | +``` |
| 169 | + |
| 170 | +Luego: |
| 171 | + |
| 172 | +```java |
| 173 | +public class App { |
| 174 | + |
| 175 | + private static final Servant jenkins = new Servant("Jenkins"); |
| 176 | + private static final Servant travis = new Servant("Travis"); |
| 177 | + |
| 178 | + /** |
| 179 | + * Program entry point. |
| 180 | + */ |
| 181 | + public static void main(String[] args) { |
| 182 | + scenario(jenkins, 1); |
| 183 | + scenario(travis, 0); |
| 184 | + } |
| 185 | + |
| 186 | + /** |
| 187 | + * Can add a List with enum Actions for variable scenarios. |
| 188 | + */ |
| 189 | + public static void scenario(Servant servant, int compliment) { |
| 190 | + var k = new King(); |
| 191 | + var q = new Queen(); |
| 192 | + |
| 193 | + var guests = List.of(k, q); |
| 194 | + |
| 195 | + // feed |
| 196 | + servant.feed(k); |
| 197 | + servant.feed(q); |
| 198 | + // serve drinks |
| 199 | + servant.giveWine(k); |
| 200 | + servant.giveWine(q); |
| 201 | + // compliment |
| 202 | + servant.giveCompliments(guests.get(compliment)); |
| 203 | + |
| 204 | + // outcome of the night |
| 205 | + guests.forEach(Royalty::changeMood); |
| 206 | + |
| 207 | + // check your luck |
| 208 | + if (servant.checkIfYouWillBeHanged(guests)) { |
| 209 | + LOGGER.info("{} will live another day", servant.name); |
| 210 | + } else { |
| 211 | + LOGGER.info("Poor {}. His days are numbered", servant.name); |
| 212 | + } |
| 213 | + } |
| 214 | +} |
| 215 | +``` |
| 216 | + |
| 217 | +La salida de la consola |
| 218 | + |
| 219 | +``` |
| 220 | +Jenkins will live another day |
| 221 | +Poor Travis. His days are numbered |
| 222 | +``` |
| 223 | + |
| 224 | + |
| 225 | +## Diagrama de clases |
| 226 | + |
| 227 | + |
| 228 | +## Aplicabilidad |
| 229 | +Utiliza el patrón Servant cuando |
| 230 | + |
| 231 | +* Cuando queremos que algunos objetos realicen una acción común y no queremos definir esta acción como un método en cada clase. |
| 232 | + |
| 233 | +## Créditos |
| 234 | + |
| 235 | +* [Let's Modify the Objects-First Approach into Design-Patterns-First](http://edu.pecinovsky.cz/papers/2006_ITiCSE_Design_Patterns_First.pdf) |
0 commit comments