GCSE Link: None

In OOP, we usually have many different classes working together, each responsible for its own part of the program. Information hiding means that each class can keep its internal details (like helper methods) private, only exposing a clear, simple interface for other classes to use.

There are three levels of access restrictions that you can place on a method or attribute:

• Public - the method or attribute can be accessed by any object of any class (no restrictions)
• Protected - the method or attribute can only be accessed by objects of the same class or subclasses
• Private - the method or attribute can only be accessed by objects of the same class

In C#, simply add the modifier (public, protected or private) before the definition (for example protected string Name = ""; or public void Output(...)). By default, everything is private.

You can even have different access modifiers for the get and set methods of an attribute. For example, public string Name {get; private set} = ""; can be read by any object (public), but only written to from the same class (private).

Class definitions can be written to show the methods and attributes of a class. The general format of a class definition is:

MyClass = Class
  Public
    Procedure Procedure1
    Function  Function1
    Var1: Integer
  Protected
    Procedure Procedure2
    Function  Function2
    Var2: String
  Private
    Procedure Procedure3
    Function  Function3
    Var3: Boolean
End

Unless explicitly stated, all attributes (variables) should be private, with separate public or protected Get and Set methods if required.

A static method is one which can be used without instantiating the class that it is part of. For example: the WriteLine() method of the Console class (you don't need to instantiate a Console object in order to use WriteLine()). They can be public, protected or private. In C#, the static keyword is added after the access modifier to mark a method as static.

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A Player class in a game has attributes Name, Health and XP, all of which have public getters and protected setters. It also has an Attack procedure and Defend method, both of which are private, and a public TakeTurn procedure.

Write the class definition for the Player class.

Player = Class
  Public
    Procedure TakeTurn
    Function  GetName
    Function  GetHealth
    Function  GetXP
  Protected
    Procedure SetName
    Procedure SetHealth
    Procedure SetXP
  Private
    Procedure Attack
    Function  Defend
    Name:   String
    Health: Integer
    XP:     Integer
End

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