Difference Between Instance and Static Methods

Let’s go through instance methods and static methods in C# — two fundamental types of methods with important differences.

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📌 1. Instance Methods

• Belong to a specific object (instance) of a class

• Can access instance fields, properties, and other instance methods

• Must be called on an object of the class

Example

public class Calculator
{
    public int Value;
 
    // Instance method
    public void Add(int number)
    {
        Value += number;
    }
}
 
Calculator calc = new Calculator();
calc.Add(5);  // Call instance method on object
Console.WriteLine(calc.Value); // 5

• Add is an instance method

• Requires calc object to call it

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📌 2. Static Methods

• Belong to the class itself, not any specific instance

• Cannot access instance fields or instance methods directly

• Called using the class name, not an object

Example

public class MathHelper
{
    // Static method
    public static int Square(int x)
    {
        return x * x;
    }
}
 
int result = MathHelper.Square(5); // Call static method
Console.WriteLine(result); // 25

• Square is a static method

• Can’t use instance members like Value unless you create an object

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📌 3. Key Differences

Feature	Instance Method	Static Method
Belongs to	Object instance	Class itself
Access to instance	Yes	No (without object)
Called using	Object (e.g., obj.Method())	Class name (e.g., Class.Method())
Can be virtual/override	Yes	No
Use case	Behaviors dependent on object state	Utility or shared behavior

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📌 4. Mixing Static and Instance

public class Circle
{
    public double Radius;
 
    public Circle(double radius)
    {
        Radius = radius;
    }
 
    // Instance method
    public double Area()
    {
        return Math.PI * Radius * Radius;
    }
 
    // Static method
    public static double CircleArea(double radius)
    {
        return Math.PI * radius * radius;
    }
}
 
Circle c = new Circle(3);
Console.WriteLine(c.Area());           // Instance method
Console.WriteLine(Circle.CircleArea(3)); // Static method

• Instance method depends on object state (Radius)

• Static method works without creating an object

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📌 5. Best Practices

1. Use instance methods when behavior depends on object data

2. Use static methods for utility/helper functions that don’t depend on object state

3. Avoid excessive use of static methods for operations that should be object-specific

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✅ Tip:

• Think: “Do I need the object’s data to do this?”

  • Yes → Instance method

  • No → Static method

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