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Decorator pattern: Improve the example
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‎decorator/README.md

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@@ -24,9 +24,9 @@ functionality.
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## Applicability
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Use Decorator
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* to add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects
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* for responsibilities that can be withdrawn
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* when extension by subclassing is impractical. Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination. Or a class definition may be hidden or otherwise unavailable for subclassing
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* To add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects
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* For responsibilities that can be withdrawn
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* When extension by subclassing is impractical. Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination. Or a class definition may be hidden or otherwise unavailable for subclassing
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## Real world examples
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* [java.io.InputStream](http://docs.oracle.com/javase/8/docs/api/java/io/InputStream.html), [java.io.OutputStream](http://docs.oracle.com/javase/8/docs/api/java/io/OutputStream.html),

‎decorator/etc/decorator.png

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‎decorator/etc/decorator.ucls

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@@ -1,66 +1,72 @@
11
<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.9" icons="true" always-add-relationships="false" generalizations="true" realizations="true"
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associations="true" dependencies="false" nesting-relationships="true" router="FAN">
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<interface id="1" language="java" name="com.iluwatar.decorator.Hostile" project="decorator"
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file="/decorator/src/main/java/com/iluwatar/decorator/Hostile.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="554" y="188"/>
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<class-diagram version="1.1.11" icons="true" automaticImage="PNG" always-add-relationships="false"
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generalizations="true" realizations="true" associations="true" dependencies="false" nesting-relationships="true"
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router="FAN">
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<class id="1" language="java" name="com.iluwatar.decorator.App" project="decorator"
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file="/decorator/src/main/java/com/iluwatar/decorator/App.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="113" width="114" x="177" y="237"/>
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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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<class id="2" language="java" name="com.iluwatar.decorator.App" project="decorator"
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file="/decorator/src/main/java/com/iluwatar/decorator/App.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="117" y="202"/>
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</class>
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<class id="2" language="java" name="com.iluwatar.decorator.SimpleTroll" project="decorator"
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file="/decorator/src/main/java/com/iluwatar/decorator/SimpleTroll.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="149" width="125" x="496" y="237"/>
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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="3" language="java" name="com.iluwatar.decorator.Troll" project="decorator"
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file="/decorator/src/main/java/com/iluwatar/decorator/Troll.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="315" y="100"/>
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<class id="3" language="java" name="com.iluwatar.decorator.ClubbedTroll" project="decorator"
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file="/decorator/src/main/java/com/iluwatar/decorator/ClubbedTroll.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="149" width="125" x="249" y="426"/>
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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="4" language="java" name="com.iluwatar.decorator.SmartHostile" project="decorator"
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file="/decorator/src/main/java/com/iluwatar/decorator/SmartHostile.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="318" y="315"/>
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<class id="4" language="java" name="com.iluwatar.decorator.TrollDecorator" project="decorator"
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file="/decorator/src/main/java/com/iluwatar/decorator/TrollDecorator.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="149" width="125" x="331" y="237"/>
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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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<dependency id="5">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="4"/>
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</dependency>
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<interface id="5" language="java" name="com.iluwatar.decorator.Troll" project="decorator"
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file="/decorator/src/main/java/com/iluwatar/decorator/Troll.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="113" width="125" x="414" y="426"/>
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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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<realization id="6">
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<end type="SOURCE" refId="4"/>
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<end type="TARGET" refId="5"/>
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</realization>
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<generalization id="7">
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<end type="SOURCE" refId="3"/>
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<end type="TARGET" refId="1"/>
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<end type="TARGET" refId="4"/>
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</generalization>
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<realization id="8">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="5"/>
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</realization>
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<association id="7">
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<association id="9">
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<end type="SOURCE" refId="4" navigable="false">
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<attribute id="8" name="decorated"/>
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<multiplicity id="9" minimum="0" maximum="1"/>
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<attribute id="10" name="decorated"/>
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<multiplicity id="11" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<end type="TARGET" refId="5" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<realization id="10">
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<end type="SOURCE" refId="4"/>
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<end type="TARGET" refId="1"/>
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</realization>
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<dependency id="11">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="3"/>
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</dependency>
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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"/>

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

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* target. Using the Decorator pattern it is possible to change the behavior of the class during
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* runtime.
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* <p>
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* In this example we show how the simple {@link Troll} first attacks and then flees the battle.
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* Then we decorate the {@link Troll} with a {@link SmartHostile} and perform the attack again. You
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* In this example we show how the simple {@link SimpleTroll} first attacks and then flees the battle.
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* Then we decorate the {@link SimpleTroll} with a {@link ClubbedTroll} and perform the attack again. You
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* can see how the behavior changes after the decoration.
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*
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*/
@@ -50,16 +50,16 @@ public static void main(String[] args) {
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// simple troll
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LOGGER.info("A simple looking troll approaches.");
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Hostile troll = new Troll();
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Troll troll = new SimpleTroll();
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troll.attack();
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troll.fleeBattle();
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LOGGER.info("Simple troll power {}.\n", troll.getAttackPower());
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// change the behavior of the simple troll by adding a decorator
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LOGGER.info("A smart looking troll surprises you.");
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Hostile smart = new SmartHostile(troll);
61-
smart.attack();
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smart.fleeBattle();
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LOGGER.info("Smart troll power {}.\n", smart.getAttackPower());
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LOGGER.info("A troll with huge club surprises you.");
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Troll clubbed = new ClubbedTroll(troll);
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clubbed.attack();
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clubbed.fleeBattle();
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LOGGER.info("Clubbed troll power {}.\n", clubbed.getAttackPower());
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}
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}

‎decorator/src/main/java/com/iluwatar/decorator/ClubbedTroll.java

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1+
/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
6+
* of this software and associated documentation files (the "Software"), to deal
7+
* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
13+
* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17+
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18+
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20+
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.decorator;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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/**
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* Decorator that adds a club for the troll
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*/
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public class ClubbedTroll extends TrollDecorator {
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private static final Logger LOGGER = LoggerFactory.getLogger(ClubbedTroll.class);
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public ClubbedTroll(Troll decorated) {
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super(decorated);
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}
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@Override
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public void attack() {
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super.attack();
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LOGGER.info("The troll swings at you with a club!");
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}
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@Override
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public int getAttackPower() {
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return super.getAttackPower() + 10;
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}
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}

‎decorator/src/main/java/com/iluwatar/decorator/Hostile.java renamed to ‎decorator/src/main/java/com/iluwatar/decorator/SimpleTroll.java

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@@ -1,38 +1,51 @@
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/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
6-
* of this software and associated documentation files (the "Software"), to deal
7-
* in the Software without restriction, including without limitation the rights
8-
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
9-
* copies of the Software, and to permit persons to whom the Software is
10-
* furnished to do so, subject to the following conditions:
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*
12-
* The above copyright notice and this permission notice shall be included in
13-
* all copies or substantial portions of the Software.
14-
*
15-
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18-
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20-
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.decorator;
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/**
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*
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* Interface for the hostile enemies.
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*
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*/
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public interface Hostile {
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void attack();
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int getAttackPower();
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void fleeBattle();
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}
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/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
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*
5+
* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
7+
* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
9+
* copies of the Software, and to permit persons to whom the Software is
10+
* furnished to do so, subject to the following conditions:
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*
12+
* The above copyright notice and this permission notice shall be included in
13+
* all copies or substantial portions of the Software.
14+
*
15+
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16+
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17+
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18+
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19+
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20+
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
21+
* THE SOFTWARE.
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*/
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package com.iluwatar.decorator;
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25+
import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
27+
28+
/**
29+
*
30+
* SimpleTroll implements {@link Troll} interface directly.
31+
*
32+
*/
33+
public class SimpleTroll implements Troll {
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private static final Logger LOGGER = LoggerFactory.getLogger(SimpleTroll.class);
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@Override
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public void attack() {
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LOGGER.info("The troll tries to grab you!");
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}
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42+
@Override
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public int getAttackPower() {
44+
return 10;
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}
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@Override
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public void fleeBattle() {
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LOGGER.info("The troll shrieks in horror and runs away!");
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}
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}

‎decorator/src/main/java/com/iluwatar/decorator/Troll.java

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@@ -1,51 +1,38 @@
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/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
4-
*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
6-
* of this software and associated documentation files (the "Software"), to deal
7-
* in the Software without restriction, including without limitation the rights
8-
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
9-
* copies of the Software, and to permit persons to whom the Software is
10-
* furnished to do so, subject to the following conditions:
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*
12-
* The above copyright notice and this permission notice shall be included in
13-
* all copies or substantial portions of the Software.
14-
*
15-
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17-
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18-
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20-
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
21-
* THE SOFTWARE.
22-
*/
23-
package com.iluwatar.decorator;
24-
25-
import org.slf4j.Logger;
26-
import org.slf4j.LoggerFactory;
27-
28-
/**
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*
30-
* Troll implements {@link Hostile} interface directly.
31-
*
32-
*/
33-
public class Troll implements Hostile {
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private static final Logger LOGGER = LoggerFactory.getLogger(Troll.class);
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@Override
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public void attack() {
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LOGGER.info("The troll swings at you with a club!");
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}
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@Override
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public int getAttackPower() {
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return 10;
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}
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47-
@Override
48-
public void fleeBattle() {
49-
LOGGER.info("The troll shrieks in horror and runs away!");
50-
}
51-
}
1+
/**
2+
* The MIT License
3+
* Copyright (c) 2014 Ilkka Seppälä
4+
*
5+
* Permission is hereby granted, free of charge, to any person obtaining a copy
6+
* of this software and associated documentation files (the "Software"), to deal
7+
* in the Software without restriction, including without limitation the rights
8+
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
9+
* copies of the Software, and to permit persons to whom the Software is
10+
* furnished to do so, subject to the following conditions:
11+
*
12+
* The above copyright notice and this permission notice shall be included in
13+
* all copies or substantial portions of the Software.
14+
*
15+
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16+
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17+
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18+
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19+
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20+
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
21+
* THE SOFTWARE.
22+
*/
23+
package com.iluwatar.decorator;
24+
25+
/**
26+
*
27+
* Interface for trolls
28+
*
29+
*/
30+
public interface Troll {
31+
32+
void attack();
33+
34+
int getAttackPower();
35+
36+
void fleeBattle();
37+
38+
}

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