Classes and objects

A class is a blueprint; an object is a runtime instance created with new. If you know Java classes, C# feels familiar—everything lives in types—but C# adds properties, value types, and reference semantics on the CLR heap.

Defining and using a class

class User {
    public string Name = "";
    public void Greet() {
        Console.WriteLine($"Hi, {Name}");
    }
}

var u = new User { Name = "Ada" };
u.Greet();

Object initializer syntax sets fields or properties at construction time. All objects are reference types unless declared as structs.

Reference semantics

User a = new User(); User b = a; — both references point to the same object; mutating through b affects a—same model as Java, unlike value-copy structs in C++ stack objects.

Important interview questions and answers

1. Q: Class vs object?
   A: Class is the type definition; object is a heap instance with its own field values.
2. Q: new keyword?
   A: Allocates memory on the managed heap and runs the constructor; GC reclaims when unreachable.

Self-check

1. What operator creates an object?
2. How does C# OOP differ from JavaScript prototypes?

Tip: Class instances are reference types on the managed heap—assigning b = a copies the reference, not the object, like Java.