IB Computer Science D.1.4 Relationships Between Objects Notes

class Printer {
    public void print(String message) {
        System.out.println(message);
    }
}

class Report {
    public void generate() {
        Printer printer = new Printer(); // used temporarily
        printer.print("Report generated");
    }
}

class Teacher {
    private String name; // attribute

    Teacher(String name) { // constructor
        this.name = name;
    }

    public String getName() { // getter
        return name;
    }
}

class Department {
    private String deptName;
    private Teacher teacher; // aggregation: Department uses Teacher

    public Department(String deptName, Teacher teacher) {
        this.deptName = deptName;
        this.teacher = teacher;
    }

    public void showDetails() {
        System.out.println("Department: " + deptName);
        System.out.println("Teacher: " + teacher.getName());
    }
    
    public static void main(String[] args) {
        Teacher t1 = new Teacher("Dr. Smith"); // teacher exists independently

        Department d1 = new Department("Computer Science", t1);

        d1.showDetails();
    }
}

class Person { // super class
    protected String name;
    protected int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public void introduce() {
        System.out.println("Hi, I am " + name + " and I am " + age + " years old.");
    }
}

class Student extends Person { // first subclass
    private String major;

    public Student(String name, int age, String major) {
        super(name, age);
        this.major = major;
    }

    public void study() {
        System.out.println(name + " is studying " + major + ".");
    }
}

class Professor extends Person { // second subclass
    private String department;

    public Professor(String name, int age, String department) {
        super(name, age);
        this.department = department;
    }

    public void teach() {
        System.out.println(name + " is teaching in the " + department + " department.");
    }
}

public class Main { // class for testing
    public static void main(String[] args) {
        Student s = new Student("Alice", 20, "Computer Science");
        Professor p = new Professor("Dr. Smith", 45, "Mathematics");

        s.introduce(); // output: Hi, I am Alice and I am 20 years old.
        s.study(); // output: Alice is studying Computer Science.

        p.introduce(); // output: Hi, I am Dr. Smith and I am 45 years old.
        p.teach(); // Dr. Smith is teaching in the Mathematics department.
    }
}