Programming Education

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Objects First

- a personal interpretation

Jens Bennedsen It-vest – networking universities It-vest – networking universities,

Denmark [email protected]

Me

• 20 years of teaching experience

– introductory programming for 20 years

– introductory object-oriented programming for 15 years

• Published 20+ articles in the area of computer

science education

– Some in collaboration with Carsten ☺

• Writing up my ph.d. thesis “Teaching and learning

programming – a model-based approach”

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Outline of the talk

• What is ”objects first”?

– CC2001

• Model-driven programming

– program in context

• Object-oriented conceptual framework

– “There is more to OO than Java”

• A model-driven introductory programming course

– progression teaching material assignments final exam

Free University, Berlin, Germay Objects First Programming Education 3

progression, teaching material, assignments, final exam, ...

• Mediation of the programming process

– How to unfold the programming process?

CC2001

• CC-2001 describes three approaches to a

program-ming first curriculum

ming first curriculum

– imperative-first – functional-first – objects-first

John Lewis: Myths about Object-Orientation and Its Pedagogy SIGCSE 2000, p. 245 - 249

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Programming Education

in Perspective

Programming Education

= Programming Methodology +

Pedagogical Design +

Programming Methodology

Programming Tools

Programming Methodology = Theory/Techniques + Process Pedagogical Design Pedagogical Design g g g = Organization + Dissemination Programming Tools = Language + Environment Programming Tools

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Many factors influence learning

Student’s learning

premises

E t

l

External

conditions

Objectives

Learning

process

Evaluation

process

Content

Hiim & Hippe 2006

Programming Methodology

• Theory/Techniques

= Theory/Techniques + Process

– model-driven development – design by contract (assertions) – patterns – ...

• Process

– incremental development Programming Methodology

incremental development – non-linearity – refactoring – test – ... Pedagogical Design

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Pedagogical Design

• Organization

= Organization + Dissemination

– graduated exposure to complexity – spiral, early bird, fill in the blanks – apprenticeship – ...

• Dissemination

– text Programming Methodology

text – labs – videos – lectures

– net-based learning objects

Pedagogical Design

A Conceptual Framework for

Object-Oriented Programming

There is more to OO than Java

There is more to OO than Java...

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Kristen Nygaard on Object-Orientation

A program execution is regarded as a physical model systemsimulating the beha ior of either a real or imaginar behavior of either a real or imaginary part of the world.

Physical modeling is based upon the conception of reality in terms of phe-nomena and concepts.

A physical model system is

construc-Free University, Berlin, Germay Objects First Programming Education 11

p y y

ted, modeling phenomena by objects and concepts by categories of objects.

Kristen Nygaard, 1926-2002

Three Perspectives on Programming

• Instructing the computer (coding)

– the purpose of programming is to instruct the computer – focus is on aspects of program execution such as storage

l t t l fl t i t

layout, control flow, parameter passing, etc.

• Managing the program description

– the purpose of programming is to create a software architecture that provides overview and understanding of the entire program – focus is on aspects such as visibility, scope, encapsulation,

modularity, software design etc.

• Conceptual modeling

– the purpose of programming is to express concepts, structure and relations

– focus is on constructs for describing concepts, phenomena and relations between these

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Conceptual Modelling

d lli Conceptual model Problem/vision concerning Specification model Program, language, abstraction abstraction modelling

concerning phenomenons

g g g

OS, machine

Problem domain Model

Overview

• Conceptual framework for object-orientation

– Concepts and modelling

Structure: aggregation association specialization – Structure: aggregation, association, specialization

– is used for organizing knowledge about a problem domain and structure in the solution domain

– Is (to some extend) supported by language constructs in OO languages

• Modelling examples

g

p

– Abstract models in UML – Implementation in Java

– Smaller examples from textbook [Barnes & Kölling] – which does not explicitly present the models...

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Association (X-a)

Relation that describes a dynamic relation between

concepts that can exist independently of each other.

MailServer keeps MailItem

Person owns Car Person rents Car

Person loves Person

Person is-friend-with Person

Student is-enrolled-at Course

Patient have-had Disease

Association in UML

MailServer keeps

*

MailItem

*

owns Person Car Student Course 0..1 owned

*

takes

*

can-drive

_*

Multiplicity (cardinality): 0..1, 1, n, a..b, 0..* (*) Role

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Association in UML (X-a)

X = keeps

MailServer

howManyMessages(String who): int getNextMailItem(String who): MailItem post(MailItem item)

MailItem

getFrom(): String getTo(): String 0..* from: String to: String message: String

post(MailItem item) getTo(): String getMessage(): String print()

Association in Java

class MailItem {

private String to; private String from; class MailServer {

Set<MailItem> messages;

private String message;

public MailItem( ... ) { ...

}

public String getFrom() { ... }

public String getTo ()

{ }

public MailServer() {

messages = new HashSet<..>(); }

public int

howManyMessages (String who) { ... }

public MailItem

getNe tMailItem (String ho) { ... }

public String getMessage() { ... }

public void print() { ... }

}

getNextMailItem (String who) { ... }

public void

post(MailItem item) { ... }

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Systematics in OOP

• Modelling

– from problem description to conceptual model

– refinement of conceptual model to specification model (method signatures and specifications)

• Implementation

– structurally: from specification model to Java code (automatically)

b d tt ib t d th d ( ti it d t ti )

– body: attributes and methods (creativity and systematics)

Problem domain

Hand-in-Hand Modeling and Coding (1)

• David Gries (Edsger W. Dijkstra)

– the loop body and the loop invariant is developed hand-in-hand with the latter leading the way

with the latter leading the way

• We (Kristen Nygaard)

– coding and class modeling is done hand-in-hand with the latter leading the way

• Design by contract and systematic programming

Design by contract and systematic programming

– a class model is a design contract in precisely the same way as a loop invariant is

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Programs as models

A program execution is regarded as

K. Nygaard

It’s not the purpose of our programs to instruct the computer; it’s the purpose of the computer

E.W. Dijkstra

p g g

a physical model system

yg

to execute our programs

Contents and Progression

• Traditional approach

– typical textbooks only address the first and to some extend the second perspective

– topics are organized according to the syntactical structures in the programming language (bottom-up)

– tendency to completeness in coverage of topics – syntax-driven progression

• Our approach

b l d f ll th i

– a balanced coverage of all three views – conceptual modeling is leading the way – systematic programming (killing rabbits) – early bird & spiral approach

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Model-Driven Progression (1)

• Model-driven

– programming tasks starts from a class model – programming tasks starts from a class model – mostly, the model is given

– sometimes, also the model must be developed

• Progression

– models become increasingly complex during the course – associated systematic programming techniques

associated systematic programming techniques – language issues covered “by need”

Course Progression

Design Conceptual model Problem/vision Specification model Implementation model Analysis Implementation

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Revealing the

Programming Process

Pointing Out the Problem

David Gries, SIGSCE 1974

What Should We Teach in an Introductory Programming Course?

“Suppose you attend a course in cabinetSuppose you attend a course in cabinet making.

The instructor briefly shows you a saw, a plane, a hammer, and a few other tools, letting you use each one for a few minutes.

He next shows you a beautifully-finished bi t

cabinet.

Finally, he tells you to design and build your own cabinet and bring him the finished product in a few weeks.

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Absurd Expectation

?

Nevertheless, this is what traditionally takes place (judged by the majority of existing textbooks)

Predictable Outcome

?

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The Missing Link...

tools concepts language constructs finished programs

?

Strategies, Principles, and Techniques

The Practice of Programming

• Describestrategies, principles, and techniques

... of problem solving and the development of programs

tools concepts language constructs finished programs q

• Demonstratehow to apply these in action

• Developprograms instead of simply

showcasing them

• Demonstratethat programming is a

non-linear process

• Demonstrateincremental development

• Demonstratemodel-driven development

D t t t t d i d l t

• Demonstratetest-driven development

• Demonstraterefactoring

• Demonstratehow to find and handle errors

• Demonstratehow to use online

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Strategies, Principles, and Techniques

D

i ti

l

... of problem solving and the development of programs

Descriptive level

(theoretical)

tools concepts language constructs finished programs

Performance level

(practical)

Video mediation

Apprenticeship learning

• Learning is an integral part of generative social

practice and through legitimate peripheral

participation

• Leve and Wenger most well-known

C P

legitimate peripheral ti i ti

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Apprenticeship

• Jordan (1989) found

– Work is the driving force. The apprentices’ progressive mastering of tasks is appreciated for “getting the problem solved ” not as a step toward a distant symbolic goal (such as a solved, not as a step toward a distant, symbolic goal (such as a certificate).

– Apprentices start with skills that are expected by the master to be easiest and where mistakes are least costly. (The tailors start out sewing, not cutting, the cloth.)

– Learning is focused on bodily performance. It involves the ability to do, rather than the ability to talk about something. It often focuses on skills rather than academic competencies

focuses on skills rather than academic competencies. – Standards of performance are embedded in the work

environment.

– Teachers and teaching are largely invisible.

Cognitive apprenticeship

• “We call this rethinking of teaching and learning in school

“cognitive apprenticeship” to emphasize two issues. First the method is aimed primarily at teaching the processes that experts use to handle complex tasks. Where conceptual and p p p factual knowledge are addressed, cognitive apprenticeship emphasizes their uses in solving problems and carrying out tasks …

Second, our term, cognitive apprenticeship, refers to the learning-through-guided-experience on cognitive and

metacognitive, rather than physical, skills and processes […] The externalization of relevant processes and methods makes possible such characteristics of apprenticeship as its reliance possible such characteristics of apprenticeship as its reliance on observation as a primary means of building a conceptual model of a complex target skill.”

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Two aspects of apprenticeship

• Person-centered aspect

– Expose the learners to how an experienced programmer works. – The master reflects and thinks aloud of the particular action,

ki th i ibl d f id tifi ti making them visible and as a source of identification. – The apprentice learns from observing the master (teacher)

performing the actions embedded in a programming practice.

• De-centered aspect

– Consider the learner as an active participant in a community of co-learners.

– The master (teacher) legitimates the skills and knowledge of the individual learner.

Nielsen and Kvale (1997)

An Example...

• Refinement of class Date

– demonstrating two principles

• The special case principlep p p public class Date {

– systematic treatment of special cases

– suppress implementation details – introduce private methods to

handle special cases

• The mañana principle

– introduce an abstraction worry about implementation

p { private int

d, // 1 <= d <= daysInMonth m, // 1 <= m <= 12 y;

public Date(int dd, int mm, int yy) { d = dd; m = mm; y = yy;

}

public void setToNextDate() { d = d + 1;

}

– worry about implementation details ”tomorrow”

• date udsnit.wmv

}

public String toString() { return d + "-" + m + "-" + y; }

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