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Added event aggregator pattern.
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‎event-aggregator/etc/classes.png‎

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‎event-aggregator/etc/classes.ucls‎

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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
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realizations="true" associations="true" dependencies="false" nesting-relationships="true">
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<class id="1" language="java" name="com.iluwatar.KingsHand" project="event-aggregator"
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file="/event-aggregator/src/main/java/com/iluwatar/KingsHand.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="805" y="431"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<interface id="2" language="java" name="com.iluwatar.EventObserver" project="event-aggregator"
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file="/event-aggregator/src/main/java/com/iluwatar/EventObserver.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="784" y="586"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</interface>
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<enumeration id="3" language="java" name="com.iluwatar.Weekday" project="event-aggregator"
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file="/event-aggregator/src/main/java/com/iluwatar/Weekday.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="437" y="195"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</enumeration>
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<class id="4" language="java" name="com.iluwatar.KingJoffrey" project="event-aggregator"
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file="/event-aggregator/src/main/java/com/iluwatar/KingJoffrey.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="380" y="413"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="5" language="java" name="com.iluwatar.LordVarys" project="event-aggregator"
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file="/event-aggregator/src/main/java/com/iluwatar/LordVarys.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="581" y="422"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="6" language="java" name="com.iluwatar.LordBaelish" project="event-aggregator"
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file="/event-aggregator/src/main/java/com/iluwatar/LordBaelish.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="1050" y="422"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="7" language="java" name="com.iluwatar.EventEmitter" project="event-aggregator"
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file="/event-aggregator/src/main/java/com/iluwatar/EventEmitter.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="1036" y="149"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="8" language="java" name="com.iluwatar.Scout" project="event-aggregator"
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file="/event-aggregator/src/main/java/com/iluwatar/Scout.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="1275" y="422"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<enumeration id="9" language="java" name="com.iluwatar.Event" project="event-aggregator"
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file="/event-aggregator/src/main/java/com/iluwatar/Event.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="721" y="159"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</enumeration>
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<realization id="10">
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<end type="SOURCE" refId="1"/>
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<end type="TARGET" refId="2"/>
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</realization>
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<association id="11">
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<bendpoint x="927" y="360"/>
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<end type="SOURCE" refId="7" navigable="false">
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<attribute id="12" name="observers"/>
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<multiplicity id="13" minimum="0" maximum="2147483647"/>
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</end>
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<end type="TARGET" refId="2" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<generalization id="14">
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<end type="SOURCE" refId="1"/>
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<end type="TARGET" refId="7"/>
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</generalization>
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<generalization id="15">
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<end type="SOURCE" refId="6"/>
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<end type="TARGET" refId="7"/>
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</generalization>
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<realization id="16">
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<end type="SOURCE" refId="4"/>
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<end type="TARGET" refId="2"/>
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</realization>
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<generalization id="17">
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<end type="SOURCE" refId="8"/>
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<end type="TARGET" refId="7"/>
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</generalization>
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<generalization id="18">
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<end type="SOURCE" refId="5"/>
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<end type="TARGET" refId="7"/>
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</generalization>
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<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</classifier-display>
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<association-display labels="true" multiplicity="true"/>
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</class-diagram>

‎event-aggregator/pom.xml‎

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<artifactId>event-aggregator</artifactId>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>

‎event-aggregator/src/main/java/com/iluwatar/App.java‎

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package com.iluwatar;
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import java.util.ArrayList;
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import java.util.List;
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/**
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*
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* The Event Aggregator pattern channels events from multiple objects
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* into a single object to simplify registration for clients.
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*
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* In the example LordBaelish, LordVarys and Scout deliver events to
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* KingsHand. KingsHand, the event aggregator, then delivers the events
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* to KingJoffrey.
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*
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*/
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public class App {
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public static void main(String[] args) {
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KingJoffrey kingJoffrey = new KingJoffrey();
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KingsHand kingsHand = new KingsHand(kingJoffrey);
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List<EventEmitter> emitters = new ArrayList<>();
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emitters.add(kingsHand);
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emitters.add(new LordBaelish(kingsHand));
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emitters.add(new LordVarys(kingsHand));
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emitters.add(new Scout(kingsHand));
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for (Weekday day: Weekday.values()) {
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for (EventEmitter emitter: emitters) {
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emitter.timePasses(day);
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}
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}
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}
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}

‎event-aggregator/src/main/java/com/iluwatar/Event.java‎

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package com.iluwatar;
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/**
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*
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* Event enumeration.
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*
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*/
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public enum Event {
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STARK_SIGHTED("Stark sighted"), WARSHIPS_APPROACHING("Warships approaching"), TRAITOR_DETECTED("Traitor detected");
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private String description;
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Event(String description) {
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this.description = description;
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}
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public String toString() {
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return description;
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}
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}

‎event-aggregator/src/main/java/com/iluwatar/EventEmitter.java‎

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package com.iluwatar;
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import java.util.LinkedList;
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import java.util.List;
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/**
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*
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* EventEmitter is the base class for event producers that can be observed.
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*
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*/
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public abstract class EventEmitter {
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private List<EventObserver> observers;
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public EventEmitter() {
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observers = new LinkedList<>();
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}
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public EventEmitter(EventObserver obs) {
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this();
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registerObserver(obs);
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}
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public void registerObserver(EventObserver obs) {
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observers.add(obs);
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}
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protected void notifyObservers(Event e) {
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for (EventObserver obs: observers) {
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obs.onEvent(e);
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}
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}
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public abstract void timePasses(Weekday day);
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}

‎event-aggregator/src/main/java/com/iluwatar/EventObserver.java‎

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package com.iluwatar;
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/**
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*
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* Observers of events implement this interface.
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*
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*/
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public interface EventObserver {
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void onEvent(Event e);
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}

‎event-aggregator/src/main/java/com/iluwatar/KingJoffrey.java‎

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package com.iluwatar;
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/**
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*
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* KingJoffrey observes events from KingsHand.
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*
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*/
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public class KingJoffrey implements EventObserver {
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@Override
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public void onEvent(Event e) {
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System.out.println("Received event from the King's Hand: " + e.toString());
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}
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}

‎event-aggregator/src/main/java/com/iluwatar/KingsHand.java‎

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package com.iluwatar;
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/**
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*
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* KingsHand observes events from multiple sources and delivers them
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* to listeners.
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*
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*/
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public class KingsHand extends EventEmitter implements EventObserver {
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public KingsHand() {
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super();
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}
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public KingsHand(EventObserver obs) {
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super(obs);
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}
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@Override
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public void onEvent(Event e) {
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notifyObservers(e);
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}
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@Override
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public void timePasses(Weekday day) {
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// NOP
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}
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}

‎event-aggregator/src/main/java/com/iluwatar/LordBaelish.java‎

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package com.iluwatar;
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/**
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*
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* LordBaelish produces events.
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*
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*/
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public class LordBaelish extends EventEmitter {
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public LordBaelish() {
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super();
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}
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public LordBaelish(EventObserver obs) {
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super(obs);
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}
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@Override
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public void timePasses(Weekday day) {
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if (day.equals(Weekday.FRIDAY)) {
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notifyObservers(Event.STARK_SIGHTED);
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}
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}
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}

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