10 minlesson

Methods in Classes

Methods in Classes

Methods define the behavior of a class - the actions that objects can perform. This lesson covers instance methods, static methods, and how they interact with object data.

Instance Methods

Instance methods operate on a specific object and can access its fields and properties:

csharp
1class Dog
2{
3    public string Name { get; set; }
4    public int Age { get; set; }
5

6    // Instance method
7    public void Bark()
8    {
9        Console.WriteLine($"{Name} says: Woof!");
10    }
11

12    // Instance method using object data
13    public void DisplayInfo()
14    {
15        Console.WriteLine($"Name: {Name}, Age: {Age}");
16    }
17}
18

19Dog myDog = new Dog { Name = "Buddy", Age = 3 };
20myDog.Bark();         // Buddy says: Woof!
21myDog.DisplayInfo();  // Name: Buddy, Age: 3

Methods with Return Values

csharp
1class Rectangle
2{
3    public double Width { get; set; }
4    public double Height { get; set; }
5

6    public double GetArea()
7    {
8        return Width * Height;
9    }
10

11    public double GetPerimeter()
12    {
13        return 2 * (Width + Height);
14    }
15

16    public bool IsSquare()
17    {
18        return Width == Height;
19    }
20}
21

22Rectangle rect = new Rectangle { Width = 5, Height = 5 };
23Console.WriteLine($"Area: {rect.GetArea()}");        // 25
24Console.WriteLine($"Perimeter: {rect.GetPerimeter()}"); // 20
25Console.WriteLine($"Is square: {rect.IsSquare()}");  // True

Methods with Parameters

csharp
1class BankAccount
2{
3    public string Owner { get; set; }
4    public decimal Balance { get; private set; }
5

6    public void Deposit(decimal amount)
7    {
8        if (amount > 0)
9        {
10            Balance += amount;
11            Console.WriteLine($"Deposited {amount:C}. New balance: {Balance:C}");
12        }
13    }
14

15    public bool Withdraw(decimal amount)
16    {
17        if (amount > 0 && amount <= Balance)
18        {
19            Balance -= amount;
20            Console.WriteLine($"Withdrew {amount:C}. New balance: {Balance:C}");
21            return true;
22        }
23        Console.WriteLine("Insufficient funds or invalid amount.");
24        return false;
25    }
26

27    public void Transfer(BankAccount destination, decimal amount)
28    {
29        if (Withdraw(amount))
30        {
31            destination.Deposit(amount);
32            Console.WriteLine($"Transferred {amount:C} to {destination.Owner}");
33        }
34    }
35}
36

37BankAccount alice = new BankAccount { Owner = "Alice" };
38BankAccount bob = new BankAccount { Owner = "Bob" };
39

40alice.Deposit(1000);
41alice.Transfer(bob, 250);

Static Methods

Static methods belong to the class, not to instances:

csharp
1class MathHelper
2{
3    // Static method - called on the class, not an object
4    public static int Add(int a, int b)
5    {
6        return a + b;
7    }
8

9    public static double CircleArea(double radius)
10    {
11        return Math.PI * radius * radius;
12    }
13

14    public static bool IsEven(int number)
15    {
16        return number % 2 == 0;
17    }
18}
19

20// Call static methods on the class name
21int sum = MathHelper.Add(5, 3);
22double area = MathHelper.CircleArea(5);
23bool even = MathHelper.IsEven(10);

Instance vs Static

csharp
1class Counter
2{
3    // Static field - shared by all instances
4    public static int TotalCount { get; private set; } = 0;
5

6    // Instance field - unique to each object
7    public int Id { get; }
8    public string Name { get; set; }
9

10    public Counter(string name)
11    {
12        TotalCount++;
13        Id = TotalCount;
14        Name = name;
15    }
16

17    // Instance method - uses object data
18    public void Display()
19    {
20        Console.WriteLine($"Counter #{Id}: {Name}");
21    }
22

23    // Static method - operates on class-level data
24    public static void ShowTotal()
25    {
26        Console.WriteLine($"Total counters created: {TotalCount}");
27    }
28}
29

30Counter c1 = new Counter("First");
31Counter c2 = new Counter("Second");
32Counter c3 = new Counter("Third");
33

34c1.Display();  // Counter #1: First
35c2.Display();  // Counter #2: Second
36

37Counter.ShowTotal();  // Total counters created: 3

Method Overloading in Classes

csharp
1class Printer
2{
3    public void Print(string message)
4    {
5        Console.WriteLine(message);
6    }
7

8    public void Print(string message, int times)
9    {
10        for (int i = 0; i < times; i++)
11        {
12            Console.WriteLine(message);
13        }
14    }
15

16    public void Print(int number)
17    {
18        Console.WriteLine($"Number: {number}");
19    }
20

21    public void Print(double number, int decimals)
22    {
23        Console.WriteLine(number.ToString($"F{decimals}"));
24    }
25}
26

27Printer p = new Printer();
28p.Print("Hello");
29p.Print("Hi", 3);
30p.Print(42);
31p.Print(3.14159, 2);  // 3.14

Methods Calling Other Methods

csharp
1class ShoppingCart
2{
3    private List<decimal> items = new List<decimal>();
4

5    public void AddItem(decimal price)
6    {
7        items.Add(price);
8    }
9

10    public decimal GetSubtotal()
11    {
12        decimal total = 0;
13        foreach (decimal price in items)
14        {
15            total += price;
16        }
17        return total;
18    }
19

20    public decimal GetTax(decimal taxRate = 0.08m)
21    {
22        return GetSubtotal() * taxRate;  // Calls GetSubtotal
23    }
24

25    public decimal GetTotal()
26    {
27        return GetSubtotal() + GetTax();  // Calls both methods
28    }
29

30    public void DisplayReceipt()
31    {
32        Console.WriteLine("=== Receipt ===");
33        Console.WriteLine($"Subtotal: {GetSubtotal():C}");
34        Console.WriteLine($"Tax: {GetTax():C}");
35        Console.WriteLine($"Total: {GetTotal():C}");
36    }
37}
38

39ShoppingCart cart = new ShoppingCart();
40cart.AddItem(19.99m);
41cart.AddItem(29.99m);
42cart.AddItem(9.99m);
43cart.DisplayReceipt();

Expression-Bodied Methods

csharp
1class Circle
2{
3    public double Radius { get; set; }
4

5    // Expression-bodied methods
6    public double GetArea() => Math.PI * Radius * Radius;
7    public double GetCircumference() => 2 * Math.PI * Radius;
8    public double GetDiameter() => Radius * 2;
9    public bool IsLargerThan(Circle other) => Radius > other.Radius;
10

11    public override string ToString() => $"Circle with radius {Radius}";
12}

Practical Example

csharp
1class Player
2{
3    public string Name { get; set; }
4    public int Health { get; private set; }
5    public int MaxHealth { get; }
6    public int Level { get; private set; }
7    public int Experience { get; private set; }
8

9    private static int nextId = 1;
10    public int Id { get; }
11

12    public Player(string name, int maxHealth = 100)
13    {
14        Id = nextId++;
15        Name = name;
16        MaxHealth = maxHealth;
17        Health = maxHealth;
18        Level = 1;
19        Experience = 0;
20    }
21

22    public void TakeDamage(int damage)
23    {
24        Health = Math.Max(0, Health - damage);
25        Console.WriteLine($"{Name} takes {damage} damage. Health: {Health}/{MaxHealth}");
26

27        if (Health == 0)
28        {
29            Console.WriteLine($"{Name} has been defeated!");
30        }
31    }
32

33    public void Heal(int amount)
34    {
35        int oldHealth = Health;
36        Health = Math.Min(MaxHealth, Health + amount);
37        int healed = Health - oldHealth;
38        Console.WriteLine($"{Name} healed for {healed}. Health: {Health}/{MaxHealth}");
39    }
40

41    public void GainExperience(int xp)
42    {
43        Experience += xp;
44        Console.WriteLine($"{Name} gained {xp} XP. Total: {Experience}");
45

46        // Level up every 100 XP
47        while (Experience >= Level * 100)
48        {
49            LevelUp();
50        }
51    }
52

53    private void LevelUp()
54    {
55        Level++;
56        Console.WriteLine($"🎉 {Name} reached Level {Level}!");
57    }
58

59    public bool IsAlive() => Health > 0;
60

61    public void DisplayStatus()
62    {
63        Console.WriteLine($"[{Id}] {Name} - Level {Level}");
64        Console.WriteLine($"    Health: {Health}/{MaxHealth}");
65        Console.WriteLine($"    Experience: {Experience}");
66    }
67}
68

69// Usage
70Player hero = new Player("Hero", 150);
71Player enemy = new Player("Goblin", 50);
72

73hero.DisplayStatus();
74hero.TakeDamage(30);
75hero.Heal(20);
76hero.GainExperience(150);  // Should level up
77hero.DisplayStatus();

Summary

In this lesson, you learned:

  • Instance methods operate on object data
  • Static methods belong to the class, not instances
  • Methods can return values and accept parameters
  • Methods can call other methods within the class
  • Overloading allows multiple methods with the same name
  • Expression-bodied syntax works for simple methods

Next, we'll learn about access modifiers for encapsulation.