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Exam Notes

Week 5: Classes and Objects in C#

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1. Classes and Objects

Class: A blueprint for creating objects, containing fields, properties, and methods.

Syntax:

public class ClassName

{

// Members (fields, properties, methods)

}

Object: An instance of a class, created using the new keyword.

Example:

ClassName obj = new ClassName();

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2. Access Modifiers

Control the accessibility of class members:

Table 17

Table 17

Modifier

Accessibility

public

Accessible from any code

internal

Accessible only within the same assembly

protected

Accessible within the class and its derived classes

private

Accessible only within the class itself

There are no rows in this table

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3. Constructors

Constructor: A special method to initialize objects, sharing the class name and having no return type.

Default Constructor: Automatically provided if no other constructor is defined; initializes fields to default values.

Parameterized Constructor: Allows setting initial values for fields.

Overloaded Constructors: Multiple constructors with different parameter lists for flexibility.

Calling Base Constructors: Use base to call a constructor from a parent class.

Syntax:

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public ChildClass(int value) : base(value) { }

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4. Fields and Properties

Fields

Variables within a class to store the object’s state.

Syntax:

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private int _age;

Properties

Use get and set to provide controlled access to fields, often including validation logic.

Auto-Implemented Properties:

Syntax:

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public int Age { get; set; }

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5. Method Overloading

Method Overloading: Allows methods with the same name but different parameter lists.

Example:

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public void Print(string text) { }

public void Print(int number) { }

Purpose: Provides flexibility to use similar methods with different inputs.

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6. Class Relationships

Composition

A "part-of" relationship where one class owns another. If the container object is destroyed, so is the contained object.

Example:

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class Car { Engine engine = new Engine(); }

Aggregation

A "has-a" relationship where one class references another without controlling its lifecycle.

Example:

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class Team { Player player; } // Team uses but doesn’t control Player

Association

A "uses-a" relationship between two independent classes without ownership.

Example:

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class Teacher { void Teach(Student student) { } }

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7. Static Members

Static Fields and Methods: Shared among all instances; belong to the class itself, not individual objects.

Syntax:

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public static int count;

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✨ Quick Study Tips

Understand Access Modifiers: Practice where each modifier applies, especially protected and internal.

Review Constructors and base Keyword: Know how constructors initialize objects and how derived classes can call parent constructors.

Differentiate Relationships: Composition vs. Aggregation, where lifecycle management is key in understanding the difference.

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