Access Modifiers

Syntax

public | private | protected | internal

Examples

public class AccessDemo
{
    public int PublicField = 1;        // accessible from anywhere
    protected int ProtectedField = 2;   // accessible in this class + subclasses
    internal int InternalField = 3;      // accessible within the same project
    private int privateField = 4;         // accessible only within this class

    private void ShowAll()
    {
        // all four are accessible from inside the class itself
        Console.WriteLine(PublicField + ProtectedField + InternalField + privateField);
    }
}

public class Account
{
    private double _balance;  // hidden from outside access

    public Account(double initialBalance)
    {
        _balance = initialBalance;
    }

    public double Balance => _balance;  // controlled read access

    public void Deposit(double amount)
    {
        if (amount > 0)
        {
            _balance += amount;
        }
    }
}

Account acc = new Account(100);
// acc._balance = -500;  // Error - private, can't be accessed directly
acc.Deposit(50);
Console.WriteLine(acc.Balance);  // 150

public class Vehicle
{
    protected int Speed;

    protected void Accelerate()
    {
        Speed += 10;
    }
}

public class Car : Vehicle
{
    public void Drive()
    {
        Accelerate();  // accessible because Car extends Vehicle
        Console.WriteLine($"Speed: {Speed}");
    }
}

Car car = new Car();
car.Drive();  // Speed: 10

Best practices

• Default to private for fields, exposing access only through public properties when genuinely needed (encapsulation)
• Use internal for types and members that should only be used within your own project/library, not exposed to external consumers
• Use protected specifically when subclasses need access, and public only for the intentional external API of a class
• Avoid the temptation to make everything public "just in case" - it removes the safety encapsulation is meant to provide

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation