Merge pull request #19 from darbyluv2code/feature/add-visitor-pattern

Add visitor pattern with course content inspection

Author: darbyluv2code

section-04-behavioral-design-patterns/15-visitor/pom.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.luv2code</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.0</version>
+
+    <properties>
+        <maven.compiler.source>25</maven.compiler.source>
+        <maven.compiler.target>25</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+</project>

section-04-behavioral-design-patterns/15-visitor/src/main/java/com/luv2code/designpatterns/behavioral/visitor/Assignment.java

@@ -0,0 +1,32 @@
+package com.luv2code.designpatterns.behavioral.visitor;
+
+/**
+ * Role: Concrete Element
+ *
+ * Represents an assignment in the course.
+ * Accepts a visitor and delegates to the correct visit method.
+ */
+public class Assignment implements CourseContent {
+
+    private String title;
+    private int estimatedCompletionMinutes;
+
+    public Assignment(String title, int estimatedCompletionMinutes) {
+        this.title = title;
+        this.estimatedCompletionMinutes = estimatedCompletionMinutes;
+    }
+
+    @Override
+    public String getTitle() {
+        return title;
+    }
+
+    public int getEstimatedCompletionMinutes() {
+        return estimatedCompletionMinutes;
+    }
+
+    @Override
+    public void accept(ContentVisitor visitor) {
+        visitor.visit(this);
+    }
+}

section-04-behavioral-design-patterns/15-visitor/src/main/java/com/luv2code/designpatterns/behavioral/visitor/ContentCountVisitor.java

@@ -0,0 +1,44 @@
+package com.luv2code.designpatterns.behavioral.visitor;
+
+/**
+ * Role: Concrete Visitor
+ *
+ * Counts how many of each content type exist in the course.
+ */
+public class ContentCountVisitor implements ContentVisitor {
+
+    private int videoCount = 0;
+    private int quizCount = 0;
+    private int assignmentCount = 0;
+
+    @Override
+    public void visit(VideoLesson videoLesson) {
+        videoCount++;
+    }
+
+    @Override
+    public void visit(Quiz quiz) {
+        quizCount++;
+    }
+
+    @Override
+    public void visit(Assignment assignment) {
+        assignmentCount++;
+    }
+
+    public int getVideoCount() {
+        return videoCount;
+    }
+
+    public int getQuizCount() {
+        return quizCount;
+    }
+
+    public int getAssignmentCount() {
+        return assignmentCount;
+    }
+}
+
+
+
+

section-04-behavioral-design-patterns/15-visitor/src/main/java/com/luv2code/designpatterns/behavioral/visitor/ContentVisitor.java

@@ -0,0 +1,20 @@
+package com.luv2code.designpatterns.behavioral.visitor;
+
+/**
+ * Role: Visitor
+ *
+ * Declares a visit method for each type of course content element.
+ * Implement this interface to add a new operation to the course content.
+ */
+public interface ContentVisitor {
+
+    // One method per element type
+    // Allows each visitor to handle each type differently
+
+    void visit(VideoLesson videoLesson);
+
+    void visit(Quiz quiz);
+
+    void visit(Assignment assignment);
+
+}

section-04-behavioral-design-patterns/15-visitor/src/main/java/com/luv2code/designpatterns/behavioral/visitor/Course.java

@@ -0,0 +1,46 @@
+package com.luv2code.designpatterns.behavioral.visitor;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Role: Object Structure
+ *
+ * Holds a collection of course content elements.
+ * Applies a visitor to each element by calling accept().
+ */
+public class Course {
+
+    private String courseName;
+    private List<CourseContent> contents;
+
+    public Course(String courseName) {
+        this.courseName = courseName;
+        this.contents = new ArrayList<>();
+    }
+
+    public String getCourseName() {
+        return courseName;
+    }
+
+    public void addContent(CourseContent theContent) {
+        contents.add(theContent);
+    }
+
+    public void accept(ContentVisitor visitor) {
+
+        for (CourseContent theContent : contents) {
+            theContent.accept(visitor); // each element then calls visitor.visit(this)
+        }
+    }
+}
+
+
+
+
+
+
+
+
+
+

section-04-behavioral-design-patterns/15-visitor/src/main/java/com/luv2code/designpatterns/behavioral/visitor/CourseContent.java

@@ -0,0 +1,15 @@
+package com.luv2code.designpatterns.behavioral.visitor;
+
+/**
+ * Role: Element
+ *
+ * Defines the contract for all course content elements.
+ * Each element must accept a visitor.
+ */
+public interface CourseContent {
+
+    String getTitle();
+
+    void accept(ContentVisitor visitor);
+
+}

section-04-behavioral-design-patterns/15-visitor/src/main/java/com/luv2code/designpatterns/behavioral/visitor/MainApp.java

@@ -0,0 +1,86 @@
+package com.luv2code.designpatterns.behavioral.visitor;
+
+/**
+ * Role: Client
+ *
+ * Demonstrates the Visitor pattern through three teaching scenarios.
+ * The course structure is built once and can accept any number of visitors.
+ */
+public class MainApp {
+
+    static void main() {
+
+        Course course = buildCourse();
+
+        System.out.println("--- Demo 1: Content Count Report ---");
+        runContentCountDemo(course);
+
+        System.out.println("\n--- Demo 2: Study Time Report ---");
+        runStudyTimeDemo(course);
+
+        System.out.println("\n--- Demo 3: Multiple Visitors on the Same Course ---");
+        runMultipleVisitorsDemo(course);
+
+    }
+
+    private static void runMultipleVisitorsDemo(Course course) {
+
+        // New visitor instances are required because
+        // each visitor accumulates state as it runs
+
+        ContentCountVisitor contentCountVisitor = new ContentCountVisitor();
+        course.accept(contentCountVisitor);
+
+        System.out.println("Course: " + course.getCourseName());
+        System.out.println("Videos: " + contentCountVisitor.getVideoCount());
+        System.out.println("Quizzes: " + contentCountVisitor.getQuizCount());
+        System.out.println("Assignments: " + contentCountVisitor.getAssignmentCount());
+
+        System.out.println();
+
+        TotalStudyTimeVisitor totalStudyTimeVisitor = new TotalStudyTimeVisitor();
+        course.accept(totalStudyTimeVisitor);
+        System.out.println("Study time: " + totalStudyTimeVisitor.getTotalMinutes() + " minutes");
+    }
+
+    private static void runStudyTimeDemo(Course course) {
+
+        TotalStudyTimeVisitor totalStudyTimeVisitor = new TotalStudyTimeVisitor();
+        course.accept(totalStudyTimeVisitor);
+
+        System.out.println("\nEstimated total study time: "
+                + totalStudyTimeVisitor.getTotalMinutes()
+                + " minutes");
+
+    }
+
+    private static void runContentCountDemo(Course course) {
+
+        ContentCountVisitor contentCountVisitor = new ContentCountVisitor();
+        course.accept(contentCountVisitor);
+
+        System.out.println("Course: " + course.getCourseName());
+        System.out.println("Videos: " + contentCountVisitor.getVideoCount());
+        System.out.println("Quizzes: " + contentCountVisitor.getQuizCount());
+        System.out.println("Assignments: " + contentCountVisitor.getAssignmentCount());
+    }
+
+    private static Course buildCourse() {
+        Course course = new Course("Master Java Design Patterns");
+
+        course.addContent(new VideoLesson("Visitor Pattern Overview", 12));
+        course.addContent(new VideoLesson("Visitor Pattern Coding Example", 15));
+        course.addContent(new Quiz("Visitor Pattern Quiz", 5));
+        course.addContent(new Assignment("Build a Visitor Implementation", 30));
+
+        return course;
+    }
+}
+
+
+
+
+
+
+
+

section-04-behavioral-design-patterns/15-visitor/src/main/java/com/luv2code/designpatterns/behavioral/visitor/Quiz.java

@@ -0,0 +1,32 @@
+package com.luv2code.designpatterns.behavioral.visitor;
+
+/**
+ * Role: Concrete Element
+ *
+ * Represents a quiz in the course.
+ * Accepts a visitor and delegates to the correct visit method.
+ */
+public class Quiz implements CourseContent {
+
+    private String title;
+    private int numberOfQuestions;
+
+    public Quiz(String title, int numberOfQuestions) {
+        this.title = title;
+        this.numberOfQuestions = numberOfQuestions;
+    }
+
+    @Override
+    public String getTitle() {
+        return title;
+    }
+
+    public int getNumberOfQuestions() {
+        return numberOfQuestions;
+    }
+
+    @Override
+    public void accept(ContentVisitor visitor) {
+        visitor.visit(this);
+    }
+}

section-04-behavioral-design-patterns/15-visitor/src/main/java/com/luv2code/designpatterns/behavioral/visitor/TotalStudyTimeVisitor.java

@@ -0,0 +1,36 @@
+package com.luv2code.designpatterns.behavioral.visitor;
+
+/**
+ * Role: Concrete Visitor
+ *
+ * Estimates the total study time for the course by summing
+ * the time for each content element.
+ */
+public class TotalStudyTimeVisitor implements ContentVisitor {
+
+    private static final int MINUTES_PER_QUESTION = 2;
+
+    private int totalMinutes = 0;
+
+    @Override
+    public void visit(VideoLesson videoLesson) {
+        System.out.println("Processing VideoLesson: " + videoLesson.getTitle());
+        totalMinutes += videoLesson.getDurationInMinutes();
+    }
+
+    @Override
+    public void visit(Quiz quiz) {
+        System.out.println("Processing Quiz: " + quiz.getTitle());
+        totalMinutes += quiz.getNumberOfQuestions() * MINUTES_PER_QUESTION;
+    }
+
+    @Override
+    public void visit(Assignment assignment) {
+        System.out.println("Processing Assignment: " + assignment.getTitle());
+        totalMinutes += assignment.getEstimatedCompletionMinutes();
+    }
+
+    public int getTotalMinutes() {
+        return totalMinutes;
+    }
+}

section-04-behavioral-design-patterns/15-visitor/src/main/java/com/luv2code/designpatterns/behavioral/visitor/VideoLesson.java

@@ -0,0 +1,32 @@
+package com.luv2code.designpatterns.behavioral.visitor;
+
+/**
+ * Role: Concrete Element
+ *
+ * Represents a video lesson in the course.
+ * Accepts a visitor and delegates to the correct visit method.
+ */
+public class VideoLesson implements CourseContent {
+
+    private String title;
+    private int durationInMinutes;
+
+    public VideoLesson(String title, int durationInMinutes) {
+        this.title = title;
+        this.durationInMinutes = durationInMinutes;
+    }
+
+    @Override
+    public String getTitle() {
+        return title;
+    }
+
+    public int getDurationInMinutes() {
+        return durationInMinutes;
+    }
+
+    @Override
+    public void accept(ContentVisitor visitor) {
+        visitor.visit(this);
+    }
+}