Какие знаете паттерны? Объясните суть перечисленных.csharp-61

public sealed class Singleton
{
    private static Singleton _instance;
    private static readonly object _lock = new object();

    private Singleton() { }

    public static Singleton Instance
    {
        get
        {
            lock (_lock)
            {
                return _instance ??= new Singleton();
            }
        }
    }
}

public abstract class Document
{
    public abstract void CreatePages();
}

public class Resume : Document
{
    public override void CreatePages()
    {
        Pages.Add(new SkillsPage());
    }
}

public interface ITarget
{
    string GetRequest();
}

public class Adaptee
{
    public string GetSpecificRequest() => "Specific request";
}

public class Adapter : ITarget
{
    private readonly Adaptee _adaptee;

    public Adapter(Adaptee adaptee) => _adaptee = adaptee;

    public string GetRequest() => _adaptee.GetSpecificRequest();
}

public interface IGraphic
{
    void Draw();
}

public class Circle : IGraphic { /*...*/ }

public class GraphicGroup : IGraphic
{
    private readonly List<IGraphic> _children = new();

    public void Add(IGraphic graphic) => _children.Add(graphic);
    public void Draw() => _children.ForEach(c => c.Draw());
}

public interface IObserver
{
    void Update(ISubject subject);
}

public class ConcreteObserver : IObserver
{
    public void Update(ISubject subject) { /*...*/ }
}

public class Subject : ISubject
{
    private readonly List<IObserver> _observers = new();

    public void Attach(IObserver observer) => _observers.Add(observer);
    public void Notify() => _observers.ForEach(o => o.Update(this));
}

public interface ISortStrategy
{
    void Sort(List<int> data);
}

public class QuickSort : ISortStrategy { /*...*/ }
public class MergeSort : ISortStrategy { /*...*/ }

public class Sorter
{
    private ISortStrategy _strategy;

    public void SetStrategy(ISortStrategy strategy) => _strategy = strategy;
    public void Sort(List<int> data) => _strategy?.Sort(data);
}

public interface IRepository<T>
{
    T GetById(int id);
    void Add(T entity);
}

public class UserRepository : IRepository<User>
{
    public User GetById(int id) { /*...*/ }
    public void Add(User entity) { /*...*/ }
}

public interface ICommandHandler<in TCommand>
{
    Task Handle(TCommand command);
}

public class CreateUserCommandHandler : ICommandHandler<CreateUserCommand>
{
    public Task Handle(CreateUserCommand command) { /*...*/ }
}

BlockingCollection<Item> _queue = new();

// Producer
Task.Run(() =>
{
    while (true)
        _queue.Add(GenerateItem());
});

// Consumer
Task.Run(() =>
{
    foreach (var item in _queue.GetConsumingEnumerable())
        ProcessItem(item);
});