The Object Pascal programming language.pptx

7/28/2019 The Object Pascal programming language.pptx

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Language overview What Turbo Pascal was

Hight level language Strongly typed

Complex structures Block structured Modularized Limited support of objects in later versions

Whats new in Object Pascal Full support of Object Oriented programming Exception handling Integrated language features to support programming under

windows


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A Simple programProgramHello;{$APPTYPE CONSOLE}

const

Min = 1;

Max = 10;

type

mytype = Integer;

var

I :MyType;

begin

forI := Min toMax do

WriteLn('Hello World!');

end.


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Lexical elements Keywords (program, begin, end, if, then, else, ...)

Reserved symbols(:=, , =, , +, - *, /, ;, :, [, ], ...)

Identifiers (Read, ReadLn, Write, WriteLn, ...) Directives (virtual, absolute, overload, override)

Numeric constants (0, 3, $FF, 3,14e+10, ...)

Character and string literals (a, #61, Hello, #20b#20)

Comments (//, (* *), { })

Directives ({$I-}, {$L X.obj}, {$IF})

Whitespaces


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Syntactic elements Declarations

Type declarations after type Variable declarations after var Contant declarations after const Procedure and function declarations

Expressions Statements

Block statement Assignment If statement While statement Repeat Statement ...


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Predifined types Integer types (Integer/Cardinal, ShortInt/Byte,

SmallInt/Word, LongInt/LongWord)

Floating Point Types (Real, Single, Double, Extended,Real48)

Separate character type

Enumerations and Sets

File types, and TextFileArrays

Strings


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String types All string types can contain the #0 character Short string types

Can only be 8bit strings Has a predifiend capacity of 255 characters or less The 0th character containts the length of the string the others are

its content This is the old Pascal string

Long string types 2 type: AnsiString, and WideString Can contain up to 2 GB characters Copy on write semantics, and reference counting

Length and SetLength can be used Compatible with the Pchar and PWideChar types


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Objects and Classes 2 keyword for declaring objects: object, and class Both declare objects Object types

Delcared with the object keyword First appeared in Turbo Pascal 7, now deprecated, maintainedmostly for backward compatibility

Works like the Record types and c++ structs Created with New, destroyed with dispose

Class types Declared with the class keyword This is the preferred object type Object Pascal Instances of Class Types are accessed trough references like in Java Constructors creates the object, and destructors destroys it All class types has a base class, when not stated, its the Tobject class


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A Class Exampletype TSomething = class (TSomeClass, ITheOne,ITheOther)

private

W :Integer;

H :Integer;protected

function GetWidth() :Integer; virtual; abstract;

procedure SetWidth(Value :Integer); override;

public

propertyWidth:Integer readGetWidthwriteSetWidth;

propertyHeight:Integer readHwriteH;

classfunctionArea(X :TSomething) :Integer;

end;


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Constructors and Destructors Constructors and destructor declared with the constructor

keyword, this way multiple constructors and destructorscan be written to the same class

Constructors can be virtual The default destructor is Destroy, Destoy called

automatically if a Constructor fails to create an object. (Thedefault constructor is Create, but it has no such afunction)

No garbage collection is done, both constructors anddestructors have to be called by hand

Objects sometimes use ownership to destroy othersautomatically


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Inheritance Object Pascal does not support multiple inheritance, only

through interfaces (like java)

The inherited keyword used to access the super class

The Self variable is the current object

Virtual Dynamic, and abstract methods can be written.

To override a virtual/dynamic method, you have to use theoverride directive, or you can choose to hide it with thereintroduce directive.

Procedures and functions declared with message (messagehandlers)directive has a special inheritance


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Message handlers Uses the message directive

Created especially to provide an easy and convinient

way of handling windows messages The inherited keyword refers to the inherited message

handler

When no message handler available the default

handler is called The Dispatch function of Tobject is used to dispatch

the message to its handler


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Properties Syntactic sugar for calling getter/setter funtions

Functions used to read and write cannot be

overloeaded Can take parameters in the form of array indices

Read, write, default, store and nodefault directives

Redeclare without type to change permissions and

visibility


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Class references The type of a class is class of type

Each class type can be used as class reference and can

be passed to functions Constructors can be called using class references, in

case of virtual constructors, the derived classconstructors will be called.

Class functions and procedures can also be calledusing class referencies (like static member functions injava and c++)

The Object Pascal programming language.pptx

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