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added Property pattern
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‎README.md‎

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@@ -15,8 +15,9 @@ Creational design patterns abstract the instantiation process. They help make a
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* [Builder](#builder)
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* [Factory Method](#factory-method)
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* [Prototype](#prototype)
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* [Property](#property)
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* [Singleton](#singleton)
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### Structural Patterns
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Structural patterns are concerned with how classes and objects are composed to form larger structures.
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**Applicability:** Use the Execute Around idiom when
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* You use an API that requires methods to be called in pairs such as open/close or allocate/deallocate.
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## <a name="property">Property</a> [&#8593;](#list-of-design-patterns)
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**Intent:** Create hierarchy of objects and new objects using already existing objects as parents.
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![alt text](https://github.com/iluwatar/java-design-patterns/blob/master/property/etc/property.jpg "Property")
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**Applicability:** Use the Property pattern when
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* when you like to have objects with dynamic set of fields and prototype inheritance
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**Real world examples:**
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* [JavaScript](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Inheritance_and_the_prototype_chain) prototype inheritance
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# Frequently asked questions
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**<a id="Q1">Q: What is the difference between State and Strategy patterns?</a>**

‎pom.xml‎

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<module>null-object</module>
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<module>event-aggregator</module>
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<module>callback</module>
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<module>execute-around</module>
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</modules>
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<module>execute-around</module>
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<module>property</module>
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</modules>
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<dependencyManagement>
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<dependencies>

‎property/etc/property.jpg‎

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‎property/etc/property.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="JPEG" always-add-relationships="false"
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generalizations="true" realizations="true" associations="true" dependencies="false" nesting-relationships="true">
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<class id="1" language="java" name="com.iluwatar.Character" project="property"
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file="/property/src/main/java/com/iluwatar/Character.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="497" y="232"/>
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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="2" language="java" name="com.iluwatar.Character.Type" project="property"
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file="/property/src/main/java/com/iluwatar/Character.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="320" y="231"/>
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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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<enumeration id="3" language="java" name="com.iluwatar.Stats" project="property"
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file="/property/src/main/java/com/iluwatar/Stats.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="695" y="205"/>
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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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<interface id="4" language="java" name="com.iluwatar.Prototype" project="property"
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file="/property/src/main/java/com/iluwatar/Prototype.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="495" y="487"/>
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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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<association id="5">
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<end type="SOURCE" refId="1" navigable="false">
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<attribute id="6" name="type"/>
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<multiplicity id="7" minimum="0" maximum="1"/>
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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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<association id="8">
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<end type="SOURCE" refId="1" navigable="false">
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<attribute id="9" name="prototype"/>
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<multiplicity id="10" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="4" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<nesting id="11">
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<end type="SOURCE" refId="1"/>
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<end type="TARGET" refId="2"/>
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</nesting>
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<realization id="12">
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<end type="SOURCE" refId="1"/>
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<end type="TARGET" refId="4"/>
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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>

‎property/pom.xml‎

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<?xml version="1.0"?>
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<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" 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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<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>property</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>

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

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package com.iluwatar;
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import com.iluwatar.Character.Type;
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/**
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* Example of Character instantiation using Property pattern (as concept also known like Prototype inheritance).
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* In prototype inheritance instead of classes, as opposite to Java class inheritance,
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* objects are used to create another objects and object hierarchies.
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* Hierarchies are created using prototype chain through delegation: every object has link to parent object.
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* Any base (parent) object can be amended at runtime (by adding or removal of some property), and all child objects will be affected as result.
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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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/* set up */
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Prototype charProto = new Character();
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charProto.set(Stats.STRENGTH, 10);
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charProto.set(Stats.AGILITY, 10);
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charProto.set(Stats.ARMOR, 10);
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charProto.set(Stats.ATTACK_POWER, 10);
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Character mageProto = new Character(Type.MAGE, charProto);
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mageProto.set(Stats.INTELLECT, 15);
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mageProto.set(Stats.SPIRIT, 10);
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Character warProto = new Character(Type.WARRIOR, charProto);
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warProto.set(Stats.RAGE, 15);
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warProto.set(Stats.ARMOR, 15); // boost default armor for warrior
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Character rogueProto = new Character(Type.ROGUE, charProto);
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rogueProto.set(Stats.ENERGY, 15);
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rogueProto.set(Stats.AGILITY, 15); // boost default agility for rogue
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/* usage */
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Character mag = new Character("Player_1", mageProto);
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mag.set(Stats.ARMOR, 8);
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System.out.println(mag);
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Character warrior = new Character("Player_2", warProto);
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System.out.println(warrior);
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Character rogue = new Character("Player_3", rogueProto);
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System.out.println(rogue);
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Character rogueDouble = new Character("Player_4", rogue);
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rogueDouble.set(Stats.ATTACK_POWER, 12);
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System.out.println(rogueDouble);
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}
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}

‎property/src/main/java/com/iluwatar/Character.java‎

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package com.iluwatar;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* Represents Character in game and his abilities (base stats).
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*/
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public class Character implements Prototype {
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public enum Type {
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WARRIOR, MAGE, ROGUE
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}
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private final Prototype prototype;
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private final Map<Stats, Integer> properties = new HashMap<>();
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private String name;
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private Type type;
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public Character() {
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this.prototype = new Prototype() { // Null-value object
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@Override
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public Integer get(Stats stat) {
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return null;
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}
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@Override
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public boolean has(Stats stat) {
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return false;
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}
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@Override
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public void set(Stats stat, Integer val) {
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}
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@Override
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public void remove(Stats stat) {
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}}
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;
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}
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public Character(Type type, Prototype prototype) {
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this.type = type;
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this.prototype = prototype;
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}
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public Character(String name, Character prototype) {
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this.name = name;
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this.type = prototype.type;
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this.prototype = prototype;
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}
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public String name() {
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return name;
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}
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public Type type() {
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return type;
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}
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@Override
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public Integer get(Stats stat) {
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boolean containsValue = properties.containsKey(stat);
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if (containsValue) {
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return properties.get(stat);
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} else {
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return prototype.get(stat);
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}
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}
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@Override
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public boolean has(Stats stat) {
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return get(stat) != null;
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}
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@Override
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public void set(Stats stat, Integer val) {
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properties.put(stat, val);
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}
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@Override
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public void remove(Stats stat) {
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properties.put(stat, null);
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}
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@Override
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public String toString() {
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StringBuilder builder = new StringBuilder();
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if (name != null) {
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builder
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.append("Player: ")
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.append(name)
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.append("\n");
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}
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if (type != null) {
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builder
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.append("Character type: ")
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.append(type.name())
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.append("\n");
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}
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builder.append("Stats:\n");
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for (Stats stat : Stats.values()) {
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Integer value = this.get(stat);
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if (value == null) {
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continue;
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}
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builder
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.append(" - ")
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.append(stat.name())
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.append(":")
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.append(value)
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.append("\n");
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}
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return builder.toString();
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}
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}

‎property/src/main/java/com/iluwatar/Prototype.java‎

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package com.iluwatar;
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/**
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* Interface for prototype inheritance
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*/
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public interface Prototype {
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public Integer get(Stats stat);
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public boolean has(Stats stat);
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public void set(Stats stat, Integer val);
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public void remove(Stats stat);
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}

‎property/src/main/java/com/iluwatar/Stats.java‎

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package com.iluwatar;
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/**
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* All possible attributes that Character can have
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*/
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public enum Stats {
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AGILITY, STRENGTH, ATTACK_POWER, ARMOR, INTELLECT, SPIRIT, ENERGY, RAGE
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}

‎property/src/test/java/com/iluwatar/AppTest.java‎

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package com.iluwatar;
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import org.junit.Test;
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public class AppTest {
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@Test
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public void test() {
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String[] args = {};
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App.main(args);
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}
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}

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