Working with Classes and Objects

public class User {
    private String name;
    private int age;

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

    public String getName() { return name; }
}

public int add(int a, int b) { return a + b; }
public <T> List<T> singleton(T item) { return List.of(item); }
public final void log(String msg) { ... }       // cannot override
public static int max(int a, int b) { ... }     // class-level
public abstract void render();                  // no body
public void deprecated() throws IOException { ... }

public class Rectangle {
    private int width, height;
    public Rectangle() { this(1, 1); }
    public Rectangle(int side) { this(side, side); }
    public Rectangle(int w, int h) { this.width = w; this.height = h; }
}

public class Config {
    static final Map<String,String> SETTINGS;
    static {
        SETTINGS = new HashMap<>();
        SETTINGS.put("env", System.getenv("APP_ENV"));
    }
}

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof User u)) return false;
    return id == u.id && Objects.equals(email, u.email);
}
@Override
public int hashCode() {
    return Objects.hash(id, email);
}