Objective 🎯

Ensure that a class has just a single instance by providing a global point of access to it.

Type ✅

❌Behavioral: Describes how objects interact/communicate between themselves.

✔️Creational: Describes how to instantiate an object without large and complex.

❌Structural: Describes how objects/classes are composed to form larger structures.

UML 📐

Participants 🔗

• Singleton:

• Responsible for creating and maintaining its own unique instance
• Defines a method to let clients to access its unique instance

Sample Code 🎮

Structural Example 🏛️

 public static class SingletonStructural
    {
        public static void Execute()
        {
            Singleton lSingleton1 = Singleton.GetInstance();
            Singleton lSingleton2 = Singleton.GetInstance();

            if(lSingleton1 == lSingleton2)
            {
                Console.WriteLine("Objects are the same instance");
                Console.WriteLine("Singleton1 HashCode: " + lSingleton1.GetHashCode());
                Console.WriteLine("Singleton2 HashCode: " + lSingleton2.GetHashCode());
            }
        }
    }

    public class Singleton
    {
        private static Singleton _Instance;

        protected Singleton()
        {
        }

        public static Singleton GetInstance()
        {
            if (_Instance == null)
                _Instance = new Singleton();

            return _Instance;
        }
    }

Output

Real-world Example 🔥

public static class SingletonPractical
    {
        public static void Execute()
        {
            LogManager lLogManager1 = LogManager.GetInstance();
            LogManager lLogManager2 = LogManager.GetInstance();

            if (lLogManager1 == lLogManager2)
            {
                Console.WriteLine("Objects are the same instance");
                Console.WriteLine("LogManager1 HashCode: " + lLogManager1.GetHashCode());
                Console.WriteLine("LogManager2 HashCode: " + lLogManager2.GetHashCode());
            }
        }
    }

    public class LogManager
    {
        private static LogManager _Instance;

        protected LogManager()
        {
        }

        public static LogManager GetInstance()
        {
            if (_Instance == null)
                _Instance = new LogManager();

            return _Instance;
        }

        public void WriteLog(string prLogMessage)
        {
            Console.WriteLine(prLogMessage);
        }
    }

Output

Source Code 🎲

github.com/VictorLins/DesignPatterns