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Commit18a1a72

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ignite1771ohbus
andauthored
iluwatar#1469 Add lambda expressions implementation for Strategy Pattern (iluwatar#1631)
*iluwatar#1469 Add Strategy Pattern lambda implementationAfter Java 8.Also take advantage of enum*iluwatar#1469 Update class diagrams*iluwatar#1469 Update README.mdAdd lambda programmatic example*iluwatar#1469 Remove unused importsCo-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com>
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‎strategy/README.md

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You cast the spell of disintegration and the dragon vaporizes in a pile of dust!
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```
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What's more, the new feature Lambda Expressions in Java 8 provides another approach for the implementation:
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```java
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publicclassLambdaStrategy {
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privatestaticfinalLoggerLOGGER=LoggerFactory.getLogger(LambdaStrategy.class);
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publicenumStrategyimplementsDragonSlayingStrategy {
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MeleeStrategy(() -> LOGGER.info(
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"WithyourExcaliburyouseverethedragon'shead!")),
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ProjectileStrategy(() -> LOGGER.info(
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"Youshootthedragonwiththemagicalcrossbowanditfallsdeadontheground!")),
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SpellStrategy(() -> LOGGER.info(
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"Youcastthespellofdisintegrationandthedragonvaporizesinapileofdust!"));
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privatefinalDragonSlayingStrategy dragonSlayingStrategy;
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Strategy(DragonSlayingStrategydragonSlayingStrategy) {
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this.dragonSlayingStrategy= dragonSlayingStrategy;
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}
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@Override
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publicvoidexecute() {
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dragonSlayingStrategy.execute();
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}
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}
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}
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```
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And here's the dragonslayer in action.
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```java
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LOGGER.info("Green dragon spotted ahead!");
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dragonSlayer.changeStrategy(LambdaStrategy.Strategy.MeleeStrategy);
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dragonSlayer.goToBattle();
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LOGGER.info("Red dragon emerges.");
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dragonSlayer.changeStrategy(LambdaStrategy.Strategy.ProjectileStrategy);
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dragonSlayer.goToBattle();
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LOGGER.info("Black dragon lands before you.");
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dragonSlayer.changeStrategy(LambdaStrategy.Strategy.SpellStrategy);
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dragonSlayer.goToBattle();
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```
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Program output is the same as above one.
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##Class diagram
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![alt text](./etc/strategy_urm.png"Strategy")

‎strategy/etc/strategy.urm.puml

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@@ -14,6 +14,19 @@ package com.iluwatar.strategy {
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interfaceDragonSlayingStrategy {
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+execute() {abstract}
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}
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classLambdaStrategy {
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-LOGGER : Logger {static}
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+LambdaStrategy()
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}
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enumStrategy {
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+MeleeStrategy {static}
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+ProjectileStrategy {static}
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+SpellStrategy {static}
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-dragonSlayingStrategy :DragonSlayingStrategy
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+execute()
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+valueOf(name : String) : Strategy {static}
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+values() : Strategy[] {static}
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}
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classMeleeStrategy {
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-LOGGER : Logger {static}
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+MeleeStrategy()
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+execute()
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}
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}
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Strategy..+LambdaStrategy
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Strategy--> "-dragonSlayingStrategy"DragonSlayingStrategy
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DragonSlayer--> "-strategy"DragonSlayingStrategy
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Strategy..|>DragonSlayingStrategy
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MeleeStrategy..|>DragonSlayingStrategy
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ProjectileStrategy..|>DragonSlayingStrategy
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SpellStrategy..|>DragonSlayingStrategy

‎strategy/etc/strategy_urm.png

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‎strategy/src/main/java/com/iluwatar/strategy/App.java

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/**
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* Program entry point.
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*
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*
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* @param args command line args
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*/
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publicstaticvoidmain(String[]args) {
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dragonSlayer.changeStrategy(newSpellStrategy());
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dragonSlayer.goToBattle();
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// Java 8 Strategy pattern
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// Java 8functional implementationStrategy pattern
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LOGGER.info("Green dragon spotted ahead!");
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dragonSlayer =newDragonSlayer(
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() ->LOGGER.info("With your Excalibur you severe the dragon's head!"));
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dragonSlayer.changeStrategy(() ->LOGGER.info(
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"You cast the spell of disintegration and the dragon vaporizes in a pile of dust!"));
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dragonSlayer.goToBattle();
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// Java 8 lambda implementation with enum Strategy pattern
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LOGGER.info("Green dragon spotted ahead!");
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dragonSlayer.changeStrategy(LambdaStrategy.Strategy.MeleeStrategy);
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dragonSlayer.goToBattle();
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LOGGER.info("Red dragon emerges.");
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dragonSlayer.changeStrategy(LambdaStrategy.Strategy.ProjectileStrategy);
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dragonSlayer.goToBattle();
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LOGGER.info("Black dragon lands before you.");
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dragonSlayer.changeStrategy(LambdaStrategy.Strategy.SpellStrategy);
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dragonSlayer.goToBattle();
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}
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}
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packagecom.iluwatar.strategy;
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importorg.slf4j.Logger;
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importorg.slf4j.LoggerFactory;
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publicclassLambdaStrategy {
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privatestaticfinalLoggerLOGGER =LoggerFactory.getLogger(LambdaStrategy.class);
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publicenumStrategyimplementsDragonSlayingStrategy {
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MeleeStrategy(() ->LOGGER.info(
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"With your Excalibur you severe the dragon's head!")),
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ProjectileStrategy(() ->LOGGER.info(
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"You shoot the dragon with the magical crossbow and it falls dead on the ground!")),
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SpellStrategy(() ->LOGGER.info(
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"You cast the spell of disintegration and the dragon vaporizes in a pile of dust!"));
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privatefinalDragonSlayingStrategydragonSlayingStrategy;
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Strategy(DragonSlayingStrategydragonSlayingStrategy) {
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this.dragonSlayingStrategy =dragonSlayingStrategy;
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}
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@Override
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publicvoidexecute() {
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dragonSlayingStrategy.execute();
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}
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}
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}

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