6. Object-Oriented Programming

Simula Project

Attempt to design a programming language that extended Algol60. Goal is to incorporate the notion of an object.

• history of object-oriented programming languages begins (1960s)

Object

entity with certain properties that control its ability to react to events in predefined ways.

1970s

rise of structured programming and top-down design (year)

1980s

Surge in interest in object-oriented programming (year)

Abstraction

collection of similar operations from two different components into a new component.

Application framework

collection of related software resources, usually in object-oriented form, that developers modify and reuse for specific application services

Polymorphism

the extension of the type of data that operations can apply to.

Encapsulation

restricting access to internal details

Smalltalk

Arose from the Dynabook Project by Alan Kay at Xerox PARC in the early 1970s, later continued by Adele Goldberg and Daniel Ingalls

Dynabook Project

was conceived as the prototype of today’s laptop and tablet computers. 

Include a WIMP (windows, icons, mouse, pull-down menus)

Message

request for a service

Receiver

object that receives a message and performs a service by invoking a method.

Parameters

Data supplied with a message by the sender.

Mutators

Messages that result in a change of state in the receiver object

Message Passing

The process of sending and receiving messages

Interface

The set of messages that an object recognizes.

Class

provides a definition of the properties and behavior of a set of objects.

Inheritance

supports the reuse of structure and behavior

Collections

containers whose elements are organized in a specific manner

Linear

 Strings, arrays, lists, stacks, and queues

Unordered

Bags, sets, and dictionaries (maps in Java)

Sorted collections

elements have natural ordering

Java

Originally designed by _ and his team at Sun Microsystems for embedded systems in appliances like microwave ovens 

• For portability and small footprint for code

• “Write once, run anywhere”

James Gosling

person who designed java along with the sun microsystems

Class

template that defined the form of an object

Objects

instances of class

Methods

subroutines that manipulate data defined by the class

Interface

set of operations on objects of a given type. 

• Glue that connects components in software systems

Dashed arrow

indicates that a class implements an interface

Solid arrow

indicates that a class extends another class and an interface extends another interface

C++

developed as an extension of C with simula-like classes.

Bjarne Stroustup

Developer of C++

Members

Instance variables (data members) and methods (member functions).

Subclasses

 referred to as derived classes

Superclasses

called base classes

Static Binding

 function called during the the compile-time of the program

• Ex. Method overloading and operator overloading

Dynamic Binding

functions called during the execution of a program

Typless Entities

 excluded from type checking

• whose class membership would be maintained separately from the type system

type constructors

Classes as _ _: making class declarations a part of the language type system. (Adopted by C++)

type system

Class as __ _ : all other structured types are excluded from the language. (Adopted by Smalltalk)

Module Mechanisms

Independent of object-oriented mechanisms

Namespace Mechanism (C++)

orthogonal to the class mechanism

Package Mechanism (Java)

allows classes to be collected into groups.

Parametric Polymorphism

Type parameters remain unspecified in declarations.

Overloading, Ad Hoc

different functions or methods share the same name but are distinguished by parameter types.

Subtype Polymorphism

Operations of one type can be applied to another type.

Inheritance

A form of subtype polymorphism that also functions as overloading on the implicit object parameter

Multi-Dispatch Problem

when inheritance and overloading do not account for binary methods. That may need overloading based on class membership in 2 or more parameters

Multimethods

Methods that can belong to more than one class

Stack Allocation

 the compiler is responsible for the automatic generation of constructor calls on entry into a block and destructor calls on exit,

Heap Allocation

explicit calls to new and delete cause constructor and destructor calls to be scheduled.

Garbage Collector

(Java, Smalltalk) - to return inaccessible storage to the heap.