Visitor pattern

README.md

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-# DesignPatternsJava9
-This repo consists Gang of Four Design patterns code on Java 9. Each branch in the repository has code of 1 design pattern. Switch repository to try out different design patterns.
+# What is Visitor Design Pattern 
+Visitor design pattern uses a visitor class which changes the executing algorithm of an element class. By this way, execution algorithm of element can vary as and when visitor varies.
+
+## Diagram
+![Diagram](https://github.com/premaseem/DesignPatternsJava9/blob/visitor-pattern/diagrams/Visitor-Pattern-class-diagram%20.png "Diagram")
+
+![Diagram](https://github.com/premaseem/DesignPatternsJava9/blob/visitor-pattern/diagrams/visitorPattern-generic.jpeg "Diagram")
+
+![Diagram](https://github.com/premaseem/DesignPatternsJava9/blob/visitor-pattern/diagrams/VisitorSequenceDiagram.png "Diagram")
+
+### When to use Visitor  Design Pattern 
+Visitor pattern is used when we have to perform an operation on a group of similar kind of Objects. With the help of visitor pattern, we can move the operational logic from the objects(Elements) to another class (Visitor class).
+
+### Learn Design Patterns with Java by Aseem Jain
+This repository contains working project code used in video Course by Packt Publication with title "Learn Design Patterns with Java " authored by "Aseem Jain".
+
+### Course link: 
+https://www.packtpub.com/application-development/learn-design-patterns-java-9-video
+
+### ![ http://in.linkedin.com/in/premaseem](https://github.com/premaseem/DesignPatternsJava9/blob/master/linkedin.png "http://in.linkedin.com/in/premaseem") Profile:  http://in.linkedin.com/in/premaseem
+
+### Authors blog on design patterns:
+https://premaseem.wordpress.com/category/computers/design-patterns/
+
+### Software Design pattern community face book page:
+https://www.facebook.com/DesignPatternGuru/
+
+### Note: 
+* This code base will work on Java 9 and above versions. 
+* `diagrams` folders carry UML diagrams
+* `pattern` folder has code of primary example. 
+* `patternBonus` folder has code of secondary or bonus example.

pattern/src/com/premaseem/ClientStudent.java

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+package com.premaseem;
+
+import java.util.Scanner;
+
+/*
+@author: Aseem Jain
+@title: Design Patterns with Java 9
+@link: https://premaseem.wordpress.com/category/computers/design-patterns/
+*/
+public class ClientStudent {
+    public static void main (String[] args) {
+        System.out.println();
+        System.out.println("University Lecture application designed using Visitor design pattern \n");
+        System.out.println("Subject available for lectures are:-");
+        System.out.println("Maths");
+        System.out.println("Computers");
+        System.out.println("Aviation");
+        System.out.println();
+        System.out.println("Please pick subject ...");
+
+        Scanner scanner = new Scanner(System.in);
+        String subjectOption = scanner.next();
+        if (subjectOption.equalsIgnoreCase("Maths")){
+            System.out.println("Math can be taught by in house Faculty");
+            Subject subject = new Maths();
+            subject.teach();
+        }
+
+        if (subjectOption.equalsIgnoreCase("Computers")){
+            System.out.println("Computers needs visiting Faculty, lets call Prof. Prem Aseem Jain :-)");
+            Subject subject = new Computer();
+            VisitingFaculty profAseem = new ProfAseem();
+            subject.acceptVisitingFacultytoTeach(profAseem);
+        }
+
+        if (subjectOption.equalsIgnoreCase("Aviation")){
+            System.out.println("Aviation needs visiting Faculty, lets call Prof. Prem Aseem Jain :-)");
+            Subject subject = new Aviation();
+            VisitingFaculty profAseem = new ProfAseem();
+            subject.acceptVisitingFacultytoTeach(profAseem);
+        }
+
+        System.out.println("Class over - Go Home and have fun :-) ");
+
+    }
+}

pattern/src/com/premaseem/Subject.java

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+package com.premaseem;
+
+/*
+@author: Aseem Jain
+@title: Design Patterns with Java 9
+@link: https://premaseem.wordpress.com/category/computers/design-patterns/
+*/
+public abstract class Subject {
+
+    abstract void acceptVisitingFacultytoTeach (VisitingFaculty visitingFaculty);
+
+    void teach(){
+           System.out.println("IN-HOUSE Faculty teaching "+ this.getClass().getSimpleName()+" subject");
+       }
+}
+
+class Aviation extends Subject{
+
+    @Override
+    void acceptVisitingFacultytoTeach (VisitingFaculty visitingFaculty) {
+        visitingFaculty.teach(this);
+    }
+}
+
+class Computer extends Subject{
+
+    @Override
+    void acceptVisitingFacultytoTeach (VisitingFaculty visitingFaculty) {
+        visitingFaculty.teach(this);
+    }
+}
+
+class Maths extends Subject{
+
+    @Override
+    void acceptVisitingFacultytoTeach (VisitingFaculty visitingFaculty) {
+        visitingFaculty.teach(this);
+    }
+}

pattern/src/com/premaseem/VisitingFaculty.java

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+package com.premaseem;
+
+/*
+@author: Aseem Jain
+@title: Design Patterns with Java 9
+@link: https://premaseem.wordpress.com/category/computers/design-patterns/
+*/
+
+public interface VisitingFaculty {
+    void teach (Aviation aviation);
+    void teach (Computer computer);
+    void teach (Maths maths);
+}
+
+class ProfAseem implements VisitingFaculty{
+
+    @Override
+    public void teach (Aviation aviation) {
+        System.out.println("Visiting Faculty teaching Aviation subject");
+    }
+
+    @Override
+    public void teach (Computer computer) {
+        System.out.println("Visiting Faculty teaching Computer subject");
+    }
+
+    @Override
+    public void teach (Maths maths) {
+        System.out.println("Visiting Faculty teaching Maths subject");
+    }
+}
+
+class AnyOtherProfessor implements VisitingFaculty{
+
+    @Override
+    public void teach (Aviation aviation) {
+        System.out.println("Visiting Faculty teaching Aviation subject");
+    }
+
+    @Override
+    public void teach (Computer computer) {
+        System.out.println("Visiting Faculty teaching Computer subject");
+    }
+
+    @Override
+    public void teach (Maths maths) {
+        System.out.println("Visiting Faculty teaching Maths subject");
+    }
+}

patternBonus/src/com/premaseem/ClientFile.java

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+package com.premaseem;
+
+import java.util.Scanner;
+
+public class ClientFile {
+
+	public static void main(String[] args) {
+
+		System.out.println("Welcome to Party host example which uses visitor pattern ");
+		Scanner scan = new Scanner(System.in);
+		Party party;
+		CookVisitorI visitorCook;
+		int repeatRunFlag = 1;
+		while (repeatRunFlag == 1) {
+			System.out.println("Which party do you want to host ");
+			System.out.println("press 1 for Loud party ");
+			System.out.println("press 2 for Silent party ");
+			int tvType = scan.nextInt();
+			if (tvType == 1) {
+				party = new LoudParty();
+			} else {
+				party = new CalmParty();
+			}
+
+			System.out.println("How would you want to manage cooking of food  ");
+			System.out.println(" Press 1 for a visitor Veg Cook ");
+			System.out.println(" Press 2 for a visitor Non- Veg Cook  ");
+			System.out.println(" Press 3 for in house cooking (no visitor) ");
+
+			int type = scan.nextInt();
+			try {
+				switch (type) {
+				case 1:
+					visitorCook = new VegCookVisitor();
+					party.accept(visitorCook);
+					break;
+				case 2:
+					visitorCook = new NonVegCookVisitor();
+					party.accept(visitorCook);
+					break;
+				case 3:
+					party.cookInHouse();
+					break;
+				}
+
+
+			} catch (Exception e1) {
+				e1.printStackTrace();
+			}
+			System.out.println("=============================");
+			System.out.println("Press 1 to Repeat .... ");
+			try {
+				repeatRunFlag = scan.nextInt();
+			} catch (Exception e) {
+				repeatRunFlag = 0;
+			}
+
+		}
+	}
+}

patternBonus/src/com/premaseem/CookVisitorI.java

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+package com.premaseem;
+
+public interface CookVisitorI {
+	void cook (LoudParty loudParty);
+	void cook (CalmParty calmParty);
+}
+
+class VegCookVisitor implements CookVisitorI{
+
+	@Override
+    public void cook(LoudParty loudParty) {
+		loudParty.meal = "Spicy Vegetables";
+		loudParty.drink = "Fruit Beer";
+		loudParty.music = "Loud music";
+		loudParty.getPartyDetail();
+    }
+
+	@Override
+    public void cook(CalmParty calmParty) {
+		calmParty.meal = "Boiled Vegetables";
+		calmParty.drink = "Fruit Juice";
+		calmParty.music = "Meditation Music";
+		calmParty.getPartyDetail();
+    }
+}
+
+class NonVegCookVisitor implements CookVisitorI{
+
+	@Override
+    public void cook(LoudParty loudParty) {
+		loudParty.meal = "Spicy chicken";
+		loudParty.drink = "Beer";
+		loudParty.music = "High Beat music";
+		loudParty.getPartyDetail();
+    }
+
+	@Override
+    public void cook(CalmParty calmParty) {
+		calmParty.meal = "Non spicy chicken";
+		calmParty.drink = "Fruit Beer";
+		calmParty.music = "Meditation music";
+		calmParty.getPartyDetail();
+    }
+}

patternBonus/src/com/premaseem/Party.java

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+package com.premaseem;
+
+public abstract class Party {
+
+	String music = " No Music";
+	String meal = " empty";
+	String drink = "plane water ";
+	CookVisitorI visitor = null;
+
+	abstract void accept(CookVisitorI visitor);
+
+
+	String getPartyDetail() {
+		String detials = visitor!= null ?visitor.getClass().getSimpleName() : "in house cooking"  + " organized " + this.getClass().getSimpleName() + " has Music : " + music + " with Drink :"
+		        + drink + " & Meal : " + meal;
+		System.out.println(detials);
+		return detials;
+	}
+
+    public void cookInHouse() {
+		meal = "Spicy Vegetables";
+		drink = "in house drink";
+		music = "DJ music";
+		getPartyDetail();	    
+    }
+
+}
+
+class LoudParty extends Party {
+
+	@Override
+	void accept(CookVisitorI visitor) {
+		this.visitor = visitor;
+		visitor.cook(this);
+	}
+}
+
+class CalmParty extends Party {
+
+	@Override
+	void accept(CookVisitorI visitor) {
+		this.visitor = visitor;
+		visitor.cook(this);
+	}
+}
+