# Singleton - Design Pattern

### 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 `📐`

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1654155940277/jyDoxh7KN.png align="left")

 
### 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  `🏛️`

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1654156024038/pxc8pt8EV.png align="left")
```csharp
 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**

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1654156184683/K6itQyeKC.png align="left")
#### Real-world Example 🔥

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1654156297427/O2Aarz7C1.png align="left")
```csharp
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**

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1654156342878/eoVq3wFpW.png align="left")
### Source Code `🎲`
https://github.com/VictorLins/DesignPatterns