Encapsulation in C#

1. Problem: Public Fields = No Control

public class Car
{
    public int Speed; // Anyone can set Speed = -500. Bad!
}
Car c = new Car();
c.Speed = -999; // Car going backwards at 999? Nonsense

2. Solution: Private Field + Public Property

public class Car
{
    private int speed; // Hidden. Only Car can touch this

    public int Speed // Public door with security check
    {
        get { return speed; }
        set
        {
            if(value >= 0) speed = value; // Block negative speed
        }
    }
}
Car c = new Car();
c.Speed = -999; // Ignored. speed stays 0
c.Speed = 100; // Works

1. Auto-Properties: Short Version

When you don't need validation, C# generates private field for you.

public class Car
{
    public string Owner { get; set; } // Auto-property
    public int Speed { get; private set; } // Read public, write private
}

2. Read-Only Properties

public class Car
{
    public string EngineNumber { get; } // Set only in constructor

    public Car(string engNum)
    {
        EngineNumber = engNum;
    }
}
// c.EngineNumber = "ABC"; // Error: read-only

3. Why Encapsulate? 3 Reasons

1. Validation: Block invalid data like negative speed
2. Change Logic Later: Change how Speed is stored without breaking code that uses it
3. Hide Complexity: User calls c.Start(), doesn't need to know engine steps

4. Full Property vs Field

private string owner; // Field: storage

public string Owner // Property: controlled access
{
    get { return owner.ToUpper(); } // Always return uppercase
    set { owner = value.Trim(); } // Remove spaces
}