Java Classes and Objects

public class Main {
    public static void main(String[] args) {
        Car a = new Car("Toyota", 2020);
        Car b = new Car("Volvo");
        a.drive(150);
        System.out.println(a.describe());
        System.out.println(b.describe());
    }
}

class Car {
    String brand;
    int year;
    int km;

    Car(String brand, int year) {
        this.brand = brand;
        this.year = year;
    }

    Car(String brand) {
        this(brand, 2026);   // call the other constructor
    }

    void drive(int distance) {
        km += distance;
    }

    String describe() {
        return brand + " (" + year + "), " + km + " km";
    }
}

import java.util.HashSet;
import java.util.List;
import java.util.Objects;

public class Main {
    public static void main(String[] args) {
        Book a = new Book("Dune", "Herbert");
        Book b = new Book("Dune", "Herbert");
        System.out.println(a);
        System.out.println(a == b);
        System.out.println(a.equals(b));
        System.out.println(new HashSet<>(List.of(a, b)).size());
    }
}

class Book {
    private final String title;
    private final String author;

    Book(String title, String author) {
        this.title = title;
        this.author = author;
    }

    @Override
    public String toString() {
        return title + " by " + author;
    }

    @Override
    public boolean equals(Object o) {
        return o instanceof Book other && title.equals(other.title) && author.equals(other.author);
    }

    @Override
    public int hashCode() {
        return Objects.hash(title, author);
    }
}