Merge pull request iluwatar#20 from sideris/master

Servant pattern

Author: iluwatar

README.md

@@ -285,6 +285,15 @@
 * there is a concurrent access in object creation, e.g. singleton, where you want to create single instance of the same class and checking if it's null or not maybe not be enough when there are two or more threads that checks if instance is null or not.
 * there is a concurrent access on a method where method's behaviour changes according to the some constraints and these constraint change within this method.
 
+##Servant
+**Intent:** Servant is used for providing some behavior to a group of classes. Instead of defining that behavior in each class - or when we cannot factor out this behavior in the common parent class - it is defined once in the Servant.
+
+![alt text](https://github.com/iluwatar/java-design-patterns/blob/master/servant/etc/servant.jpg "Servant")
+
+**Applicability:** Use the Servant pattern when
+* When we want some objects to perform a common action and don't want to define this action as a method in every class.
+
+
 # Frequently asked questions
 
 **Q: What is the difference between State and Strategy patterns?**

pom.xml

@@ -36,6 +36,7 @@
     <module>template-method</module>
     <module>visitor</module>
     <module>double-checked-locking</module>
+    <module>servant</module>
   </modules>
 
 <build>
@@ -53,4 +54,4 @@
 	</plugins>
 </build>
 
-</project>
+</project>

servant/etc/servant.jpg

@@ -0,0 +1,21 @@
+<?xml version="1.0"?>
+<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"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>servant</artifactId>
+  <name>servant</name>
+  <url>http://maven.apache.org</url>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>3.8.1</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

servant/etc/servant.svg

@@ -0,0 +1,53 @@
+package com.iluwatar;
+
+import java.util.ArrayList;
+
+
+/**
+ * Servant offers some functionality to a group of classes without defining that functionality in each of them. 
+ * A Servant is a class whose instance provides methods that take care of a desired service,
+ * while objects for which the servant does something, are taken as parameters.
+ *
+ */
+public class App {
+	static Servant jenkins = new Servant("Jenkins");
+	static Servant travis = new Servant("Travis");
+	
+	public static void main( String[] args ){
+		scenario(jenkins, 1);
+		scenario(travis, 0);
+	}
+	
+	/*
+	 * Can add a List with enum Actions for variable scenarios
+	 * */
+	public static void scenario(Servant servant, int compliment){
+		King k = new King();
+		Queen q = new Queen();
+		
+		ArrayList<Royalty> guests = new ArrayList<>();
+		guests.add(k);
+		guests.add(q);
+		
+		//feed
+		servant.feed(k);
+		servant.feed(q);
+		//serve drinks
+		servant.giveWine(k);
+		servant.giveWine(q);
+		//compliment
+		servant.GiveCompliments( guests.get(compliment) );
+		
+		//outcome of the night
+		for(Royalty r : guests)
+			r.changeMood();
+		
+		//check your luck
+		if( servant.checkIfYouWillBeHanged(guests) )
+			System.out.println(servant.name + " will live another day");
+		else
+			System.out.println("Poor " + servant.name + ". His days are numbered");
+	}
+	
+	
+}

servant/etc/servant.xml

@@ -0,0 +1,31 @@
+package com.iluwatar;
+
+public class King implements Royalty{
+	private boolean isDrunk = false, isHungry = true, isHappy = false;
+	private boolean complimentReceived = false;
+	
+	@Override
+	public void getFed() {
+		isHungry = false;
+	}
+
+	@Override
+	public void getDrink() {
+		isDrunk = true;
+	}
+	
+	public void receiveCompliments(){
+		complimentReceived = true;
+	}
+
+	@Override
+	public void changeMood() {
+		if(!isHungry && isDrunk) isHappy = true;
+		if( complimentReceived ) isHappy = false;
+	}
+
+	@Override
+	public boolean getMood() {
+		return isHappy;
+	}
+}

servant/pom.xml

@@ -0,0 +1,35 @@
+package com.iluwatar;
+
+public class Queen implements Royalty{
+	private boolean isDrunk = true, isHungry = false, isHappy = false;
+	private boolean isFlirty = true, complimentReceived = false;
+	
+	@Override
+	public void getFed() {
+		isHungry = false;
+	}
+
+	@Override
+	public void getDrink() {
+		isDrunk = true;
+	}
+	
+	public void receiveCompliments(){
+		complimentReceived = true;
+	}
+
+	@Override
+	public void changeMood() {
+		if( complimentReceived && isFlirty && isDrunk ) isHappy = true;
+	}
+
+	@Override
+	public boolean getMood() {
+		return isHappy;
+	}
+	
+	public void setFlirtiness(boolean f){
+		this.isFlirty = f;
+	}
+
+}

servant/src/etc/servant.jpg

@@ -0,0 +1,9 @@
+package com.iluwatar;
+
+interface Royalty {
+	public void getFed();
+	public void getDrink();
+	public void changeMood();
+	public void receiveCompliments();
+	public boolean getMood();
+}

servant/src/etc/servant.svg

@@ -0,0 +1,31 @@
+package com.iluwatar;
+
+import java.util.ArrayList;
+
+public class Servant {
+	public String name;
+	
+	public Servant(String name){
+		this.name = name;
+	}
+
+	public void feed(Royalty r){
+		r.getFed();
+	}
+	
+	public void giveWine(Royalty r){
+		r.getDrink();
+	}
+	
+	public void GiveCompliments(Royalty r){
+		r.receiveCompliments();
+	}
+	
+	public boolean checkIfYouWillBeHanged(ArrayList<Royalty> tableGuests){
+		boolean anotherDay = true;
+		for( Royalty r : tableGuests )
+			if( !r.getMood() ) anotherDay = false;
+			
+		return anotherDay;
+	}
+}