Objects & classes — the big idea

Until now your data (variables) and your actions (procedures) lived apart. Object-oriented programming (OOP) packs them together: a class is the blueprint, an object is one real thing built from it.

type
  TLearner = class
  private
    fName : String;              // attributes (fields) - hidden
    fMark : Integer;
  public
    constructor Create(sName : String; iMark : Integer);
    function GetName : String;   // accessor ("getter")
    procedure SetName(sName : String);  // mutator ("setter")
    function ToString : String;
  end;

The vocabulary you must own for Paper 1 and Paper 2 theory:

• Class — the blueprint (TLearner). By convention class names start with T.
• Object — one instance built from the blueprint: objL := TLearner.Create('Anele', 90);
• Attributes / fields — the object's own variables, prefixed f, declared private.
• Encapsulation — fields are private; the outside world must use public methods. The class guards its own data.
• Constructor — the special method (Create) that builds and initialises a new object.
• Accessor / mutator — GetX returns a field's value; SetX changes it (often with validation).
• toString — returns a neat String describing the object, ready for a memo or message.

In the exam the class usually lives in its own unit; the form unit creates and uses the objects. Here we keep them in one editor so you can see everything at once.