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Ilkka Seppälä 2020-09-13 18:15:17 +03:00
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strategy/README.md
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@ -9,17 +9,20 @@ tags:
--- ---
## Also known as ## Also known as
Policy Policy
## Intent ## Intent
Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary
independently from clients that use it. Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets
the algorithm vary independently from clients that use it.
## Explanation ## Explanation
Real world example Real world example
> Slaying dragons is a dangerous profession. With experience it becomes easier. Veteran dragonslayers have developed different fighting strategies against different types of dragons. > Slaying dragons is a dangerous job. With experience it becomes easier. Veteran
> dragonslayers have developed different fighting strategies against different types of dragons.
In plain words In plain words
@ -27,7 +30,8 @@ In plain words
Wikipedia says Wikipedia says
> In computer programming, the strategy pattern (also known as the policy pattern) is a behavioral software design pattern that enables selecting an algorithm at runtime. > In computer programming, the strategy pattern (also known as the policy pattern) is a behavioral
> software design pattern that enables selecting an algorithm at runtime.
**Programmatic Example** **Programmatic Example**
@ -71,7 +75,8 @@ public class SpellStrategy implements DragonSlayingStrategy {
} }
``` ```
And here is the mighty dragonslayer who is able to pick his fighting strategy based on the opponent. And here is the mighty dragonslayer, who is able to pick his fighting strategy based on the
opponent.
```java ```java
public class DragonSlayer { public class DragonSlayer {
@ -92,7 +97,7 @@ public class DragonSlayer {
} }
``` ```
Finally here's dragonslayer in action. Finally here's the dragonslayer in action.
```java ```java
LOGGER.info("Green dragon spotted ahead!"); LOGGER.info("Green dragon spotted ahead!");
@ -104,19 +109,25 @@ Finally here's dragonslayer in action.
LOGGER.info("Black dragon lands before you."); LOGGER.info("Black dragon lands before you.");
dragonSlayer.changeStrategy(new SpellStrategy()); dragonSlayer.changeStrategy(new SpellStrategy());
dragonSlayer.goToBattle(); dragonSlayer.goToBattle();
```
// Green dragon spotted ahead!
// With your Excalibur you sever the dragon's head! Program output:
// Red dragon emerges.
// You shoot the dragon with the magical crossbow and it falls dead on the ground! ```
// Black dragon lands before you. Green dragon spotted ahead!
// You cast the spell of disintegration and the dragon vaporizes in a pile of dust! With your Excalibur you sever the dragon's head!
Red dragon emerges.
You shoot the dragon with the magical crossbow and it falls dead on the ground!
Black dragon lands before you.
You cast the spell of disintegration and the dragon vaporizes in a pile of dust!
``` ```
## Class diagram ## Class diagram
![alt text](./etc/strategy_1.png "Strategy")
![alt text](./etc/strategy_urm.png "Strategy")
## Applicability ## Applicability
Use the Strategy pattern when Use the Strategy pattern when
* Many related classes differ only in their behavior. Strategies provide a way to configure a class either one of many behaviors * Many related classes differ only in their behavior. Strategies provide a way to configure a class either one of many behaviors

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strategy/etc/strategy.ucls
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<?xml version="1.0" encoding="UTF-8"?>
<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
realizations="true" associations="true" dependencies="false" nesting-relationships="true">
<interface id="1" language="java" name="com.iluwatar.strategy.DragonSlayingStrategy" project="strategy"
file="/strategy/src/main/java/com/iluwatar/strategy/DragonSlayingStrategy.java" binary="false" corner="BOTTOM_RIGHT">
<position height="88" width="186" x="525" y="428"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</interface>
<class id="2" language="java" name="com.iluwatar.strategy.ProjectileStrategy" project="strategy"
file="/strategy/src/main/java/com/iluwatar/strategy/ProjectileStrategy.java" binary="false" corner="BOTTOM_RIGHT">
<position height="106" width="151" x="218" y="264"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="3" language="java" name="com.iluwatar.strategy.SpellStrategy" project="strategy"
file="/strategy/src/main/java/com/iluwatar/strategy/SpellStrategy.java" binary="false" corner="BOTTOM_RIGHT">
<position height="106" width="125" x="409" y="264"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="4" language="java" name="com.iluwatar.strategy.DragonSlayer" project="strategy"
file="/strategy/src/main/java/com/iluwatar/strategy/DragonSlayer.java" binary="false" corner="BOTTOM_RIGHT">
<position height="124" width="284" x="574" y="264"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="5" language="java" name="com.iluwatar.strategy.MeleeStrategy" project="strategy"
file="/strategy/src/main/java/com/iluwatar/strategy/MeleeStrategy.java" binary="false" corner="BOTTOM_RIGHT">
<position height="106" width="127" x="898" y="264"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<realization id="6">
<end type="SOURCE" refId="5"/>
<end type="TARGET" refId="1"/>
</realization>
<realization id="7">
<end type="SOURCE" refId="2"/>
<end type="TARGET" refId="1"/>
</realization>
<realization id="8">
<end type="SOURCE" refId="3"/>
<end type="TARGET" refId="1"/>
</realization>
<association id="9">
<end type="SOURCE" refId="4" navigable="false">
<attribute id="10" name="strategy"/>
<multiplicity id="11" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="1" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</classifier-display>
<association-display labels="true" multiplicity="true"/>
</class-diagram>

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