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copied!<p>You're still missing the essential point: a <em>class</em> associates the data <em>with its methods.</em> So the method that sets Jim's teacher is part of the Student class, as is the method that sets Jim's grade.</p> <p>Think of it in natural language first. "Jim is a student; students have names, stident ID numbers, and classes. Classes have teachers and classrooms. Students receive grades for each class at the end of the term."</p> <p>So we have a class Student. Student, when you create an object from it, needs the students name and student ID, so the "constructor" needs to be something with a name string and a student ID -- call it a String too -- to initialize it. I don't know C#, so I'll make a pseudocde with braces...</p> <pre><code>class Student { String name; String studentID; Course crsList = List<Course>; // "list of courses." Student(String name, String studentID ){ // Make a new student, the "constructor" this.name = name; this.studentID = studentID; } addCourse(Course c){ // Add a course to the student's list this.crsList.append(c); // Adds c to end of crsList } } </code></pre> <p>This says "A Student has a name and ID, and we can add classes to their collection of classes."</p> <pre><code>class Teacher { String name; Course crsList = List<Course>; Teacher(String name){ this.name = name; } // ... more methods here. } </code></pre> <p>But we observe that teachers and students are both kinds of people, so we "refactor" this to put the common piece together</p> <pre><code>class Person { String name; Person(String name){ this.name = name; } // ... more methods } </code></pre> <p>Now we change Teacher and Student so we say</p> <pre><code>class Student : Person { String studentID; Student(String name, String studentID){ // Now we need to initialize the Person part super(name); // and the special Student part this.studentID = studentID; } } </code></pre> <p>which now says "a Student is a kind of Person who has an additional student ID, and who we can add classes to."</p> <p>You'd go on to define "addClass" for Teach, <em>but as part of the Teacher class</em>. Why? Because adding a class for a teacher means something different than adding one for a student. You'd add a method to Student that takes a Course and a Grade, finds the Course and assigns he grade somehow. (Pop quiz: is a Grade part of a Course or part of a Student?)</p>

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