OOP Introduction and UML Class Diagram

//abstract class: Animal defines basic features of animals

abstract class Animal{
    //Encapsulation: Private variable to protect state
    private String name;

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

    //abstrac method: each animal's sound
    public abstract void makeSound();

    //encapsulation: Getter method to access name
    public String getName(){
        return name;
    }
}

//inheritance: dog class inherits from animal
class Dog extends Animal {
    public Dog(String name){
        super(name); //call parent class constructor 
    }

    //implement abstract method

    @Override
    public void makeSound() {
        System.out.println(getName() + "says woof!");
    }
}

//inheritance: cat class inherits from animal
class Cat extends Animal{
    public Cat(String name){
        super(name); //call parent class constructor
    }
    //implement abstract method

    @Override
    public void makeSound(){
        System.out.println(getName() + "says Meow!~");
    }
}

//main class: AnimalTest for testing the program 
public class AnimalTest{
    public static void main(String[] args){
        //polmorphism: using parent type to reference child objects 
        Animal dog_1 = new Dog("Buddy");
        Animal cat_1 = new Cat("Whiskers");

        //call method (message)

        dog_1.makeSound();
        cat_1.makeSound();

    }
}

//public class
public class Student{
    //class attributes 
    String name;
    int age;
    int studentID;

    //constructor to initialize a new student object 
    public Stdudent(String name,int age, int studentID){
        this.name = name;
        this.age = age;
        this.studentID = studentID;
    }

    //method to display the student's information 
    public void displayInfo(){
        System.out.println("Student Information: ");
        System.out.println("Name: " + name);
        System.out.println("Name: " + age);
        System.out.println("Name: " + studentID);
    }
}

public class Main{
    public static void main (String[] args){

        //create a first student object 
        Student student_1 = new Student("Duke HSu", 20, 1001);
        Student student_2 = new Student("Six", 21, 1002);

        //call student class method - displayInfo()
        System.out.println("Student 1 Details: ");
        student_1.displayInfo(); //message = object + method

        System.out.println("Student 2 Details: ");
        student_2.displayInfo(); 
    }
}

// Car class define the structure of a car
class Car{
    //instance data value: color and model as public
    public String color;
    public String model;

    //constructor to initialize the instance data values
    public Car(String color, String model){
        this.color = color;
        this.model = model;
    }

    //method to display car detiles 
    public void displayDetails(){
        System.out.println("Car model: " + model);
        System.out.println("Car color: " + color);

    }
}


public class CarTest {
    public static void main(String[] args){
        //create different car object(instances)
        Car car1 = new Car("Red","Toyota");
        Car car2 = new Car("Blue", "Honda");


        //call method
        car1.displayDetails(); //red toyota
        car2.displayDetails(); //blue honda

        //change colors directly since they are public
        car1.color = "Black";
        car2.color = "White";

        //display update detailes
        car1.displayDetails();
        car2.displayDetails();




    }

}