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Merge branch 'add-delegation-pattern'
* add-delegation-pattern: Add java documentation iluwatar#324 Populate the index.md for the delegate module iluwatar#324 Move App.java to correct Package iluwatar#324 Move App.java to correct Package iluwatar#324 Generic For AbstractPrinterController iluwatar#324 Generate UML for delegation pattern Add simple tests for delegate pattern iluwatar#324 Make AppTest.java match other patterns and update AppTest.java to match other patterns iluwatar#324 3am Code is starting to show. Get this build working. iluwatar#324 Created a unit test for build, added junit to pom for delegation maven module. iluwatar#324 Add template index.md for population later iluwatar#324 Added skeleton code for delegation pattern iluwatar#324 Create maven module for delegation pattern iluwatar#324
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‎delegation/etc/delegation.png‎

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‎delegation/etc/delegation.ucls‎

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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.9" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
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realizations="true" associations="true" dependencies="false" nesting-relationships="true" router="FAN">
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<interface id="1" language="java" name="com.iluwatar.delegation.simple.Printer" project="delegation"
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file="/delegation/src/main/java/com/iluwatar/delegation/simple/Printer.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="362" y="84"/>
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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.delegation.simple.AbstractPrinterController" project="delegation"
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file="/delegation/src/main/java/com/iluwatar/delegation/simple/AbstractPrinterController.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="97" width="191" x="41" y="37"/>
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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.delegation.simple.PrinterController" project="delegation"
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file="/delegation/src/main/java/com/iluwatar/delegation/simple/PrinterController.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="136" y="214"/>
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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.delegation.simple.printers.HPPrinter" project="delegation"
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file="/delegation/src/main/java/com/iluwatar/delegation/simple/printers/HPPrinter.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="187" y="333"/>
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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.delegation.simple.printers.EpsonPrinter" project="delegation"
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file="/delegation/src/main/java/com/iluwatar/delegation/simple/printers/EpsonPrinter.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="362" y="333"/>
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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.delegation.simple.printers.CanonPrinter" project="delegation"
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file="/delegation/src/main/java/com/iluwatar/delegation/simple/printers/CanonPrinter.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="537" y="333"/>
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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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<generalization id="7">
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<end type="SOURCE" refId="3"/>
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<end type="TARGET" refId="2"/>
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</generalization>
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<realization id="8">
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<end type="SOURCE" refId="5"/>
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<end type="TARGET" refId="1"/>
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</realization>
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<realization id="9">
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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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<association id="10">
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<end type="SOURCE" refId="2" navigable="false">
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<attribute id="11" name="printer"/>
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<multiplicity id="12" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<realization id="13">
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<end type="SOURCE" refId="6"/>
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<end type="TARGET" refId="1"/>
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</realization>
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<realization id="14">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="1"/>
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</realization>
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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>

‎delegation/index.md‎

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---
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layout: pattern
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title: Delegation
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folder: delegation
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permalink: /patterns/delegation/
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categories: Behavioral
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tags:
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- Java
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- Difficulty-Beginner
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---
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**Also known as:** Proxy Chains
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**Intent:** It is a technique where an object expresses certain behavior to the outside but in
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reality delegates responsibility for implementing that behaviour to an associated object.
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![alt text](./etc/delegation.png "Delegate")
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**Applicability:** Use the Delegate pattern in order to achieve the following
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* Reduce the coupling of methods to their class
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* Components that behave identically, but realize that this situation can change in the future.
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**Credits**
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* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)

‎delegation/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<!--
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~ The MIT License (MIT)
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~
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~ Copyright (c) 2015 Orange Foundry
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~
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~ 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
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~ 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
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~ 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,
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~ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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~ 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,
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~ 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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<project xmlns="http://maven.apache.org/POM/4.0.0"
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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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<parent>
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<artifactId>java-design-patterns</artifactId>
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<groupId>com.iluwatar</groupId>
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<version>1.9.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>delegation</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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<dependency>
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<groupId>com.github.stefanbirkner</groupId>
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<artifactId>system-rules</artifactId>
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<version>1.14.0</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>

‎delegation/src/main/java/com/iluwatar/delegation/simple/AbstractPrinterController.java‎

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package com.iluwatar.delegation.simple;
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/**
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* Extra layer of abstraction for the controller to allow the controller in this example {@link PrinterController} to
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* be as clean as possible. This just provides the default constructor and a simple getter method. The generic of T allows
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* any implementation of {@link Printer}
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*
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* @param <T> Printer
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* @see Printer
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* @see PrinterController
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*/
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public abstract class AbstractPrinterController<T extends Printer> implements Printer {
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private T printer;
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/**
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* @param printer instance of T {@link Printer} this instance is the delegate
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*/
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public AbstractPrinterController(T printer) {
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this.printer = printer;
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}
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/**
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* Helper method to return the current instance of T {@link Printer} in order for
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* the controller to call operations on the {@link Printer}
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*
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* @return instance of Printer
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* @see Printer
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*/
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protected T getPrinter() {
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return printer;
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}
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}

‎delegation/src/main/java/com/iluwatar/delegation/simple/App.java‎

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package com.iluwatar.delegation.simple;
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import com.iluwatar.delegation.simple.printers.CanonPrinter;
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import com.iluwatar.delegation.simple.printers.EpsonPrinter;
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import com.iluwatar.delegation.simple.printers.HPPrinter;
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/**
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* In this example the delegates are {@link EpsonPrinter}, {@link HPPrinter} and {@link CanonPrinter} they all implement
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* {@link Printer}. The {@link AbstractPrinterController} and through inheritance {@link PrinterController} also implement
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* {@link Printer}. However neither provide the functionality of {@link Printer} by printing to the screen, they actually
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* call upon the instance of {@link Printer} that they were instantiated with. Therefore delegating the behaviour to
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* another class.
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*/
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public class App {
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public static final String MESSAGE_TO_PRINT = "hello world";
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/**
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* Program entry point
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*
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* @param args command line args
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*/
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public static void main(String[] args) {
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AbstractPrinterController hpPrinterController = new PrinterController(new HPPrinter());
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AbstractPrinterController canonPrinterController = new PrinterController(new CanonPrinter());
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AbstractPrinterController epsonPrinterController = new PrinterController(new EpsonPrinter());
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hpPrinterController.print(MESSAGE_TO_PRINT);
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canonPrinterController.print(MESSAGE_TO_PRINT);
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epsonPrinterController.print(MESSAGE_TO_PRINT);
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}
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}

‎delegation/src/main/java/com/iluwatar/delegation/simple/Printer.java‎

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package com.iluwatar.delegation.simple;
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/**
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* Interface that both the Controller and the Delegate will implement.
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*
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* @see com.iluwatar.delegation.simple.printers.CanonPrinter
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* @see com.iluwatar.delegation.simple.printers.EpsonPrinter
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* @see com.iluwatar.delegation.simple.printers.HPPrinter
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* @see AbstractPrinterController
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*/
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public interface Printer {
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/**
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* Method that takes a String to print to the screen. This will be implemented on both the
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* controller and the delegate allowing the controller to call the same method on the delegate class.
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*
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* @param message to be printed to the screen
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*/
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void print(final String message);
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}

‎delegation/src/main/java/com/iluwatar/delegation/simple/PrinterController.java‎

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package com.iluwatar.delegation.simple;
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public class PrinterController extends AbstractPrinterController {
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public PrinterController(Printer printer) {
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super(printer);
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}
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/**
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* This method is implemented from {@link Printer} however instead on providing an
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* implementation, it instead calls upon the class passed through the constructor. This is the delegate,
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* hence the pattern. Therefore meaning that the caller does not care of the implementing class only the owning
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* controller.
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*
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* @param message to be printed to the screen
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*/
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@Override
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public void print(String message) {
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getPrinter().print(message);
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}
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}

‎delegation/src/main/java/com/iluwatar/delegation/simple/printers/CanonPrinter.java‎

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package com.iluwatar.delegation.simple.printers;
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import com.iluwatar.delegation.simple.Printer;
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/**
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* Specialised Implementation of {@link Printer} for a Canon Printer, in
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* this case the message to be printed is appended to "Canon Printer : "
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*
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* @see Printer
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*/
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public class CanonPrinter implements Printer {
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/**
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* {@inheritDoc}
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*/
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@Override
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public void print(String message) {
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System.out.println("Canon Printer : " + message);
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}
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}

‎delegation/src/main/java/com/iluwatar/delegation/simple/printers/EpsonPrinter.java‎

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package com.iluwatar.delegation.simple.printers;
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import com.iluwatar.delegation.simple.Printer;
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/**
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* Specialised Implementation of {@link Printer} for a Epson Printer, in
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* this case the message to be printed is appended to "Epson Printer : "
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*
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* @see Printer
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*/
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public class EpsonPrinter implements Printer{
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/**
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* {@inheritDoc}
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*/
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@Override
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public void print(String message) {
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System.out.println("Epson Printer : " + message);
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}
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}

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