On Object Oriented modeling in Java (Why

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On Object Oriented modeling in Java (Why
How)Ana Madevska BogdanovaInstitute of
informaticsFaculty of Natural Sciences and
MathematicsSkopje, Macedonia
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Agenda

• The motivation
• The need of introducing design patterns in the
  first year of studies
• Incorporation in the concepts of the existing OOP
  course
• Expected results

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The motivation

• To start earlier with Java (DSA will improve)
• To introduce design patterns in OOP

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The motivation

• The first two courses
• Structured programming
• Object oriented and visual programming
• C is the represent of a OOP language
• The second course
• Encaptulation
• Inheritance
• Polymorphism

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Where is Java in the curriculum?

• Java is in the course Data Structures and
  Algorithms
• Third semester
• The course is too much
• Introductory level of Java while listening to the
  theory about Data structures
• Discrepancy between programming the data
  structures and the theory
• Solution?

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The solution

• We will introduce Java in the second semester
  within the course OO programming
• The students are ready to start to program data
  structures immediately within the course DSA
• No discrepancy

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Agenda

• The motivation
• The need of introducing design patterns in the
  first year of studies
• Incorporation in the concepts of the existing OOP
  course
• Expected results

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Another existing problem

• Thinking in the design pattern level
• Introduced in the course of software engineering
  in the 5th semester
• Software design and architecture
• In the first two programming courses the students
  mind is focused only on technical clarity in
  developing the OO system

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Idea introduce design patterns in the first
semester

• In the OO programming course we can introduce
  some problems and discuss them with the students
• How to create OO model to go through the
  process OO modeling

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Why do that?

• Till now
• We give them ready OO model and ask the students
  to program it and use
• Encaptulation
• Polymorphism
• Inheritance
• New idea
• Ask the students to BUILD the OO model for a
  given problem
• To broaden their point of view for the proper
  programming
• To be ready to learn more design patterns in the
  latter courses

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The levels

• 1. OO basics
• encapsultion, polymorphism, inheritance
• 2. OO principles
• 3. OO patterns
• 1. Strategy
• Defines a family of algorithms, encapsulates each
  one, and makes them interchangable
• - let the algorithm vary independently from
  clients that use it

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Why design patterns?

• This is what the students should learn in the
  first year of their studies.
• Students learn that applying design patterns is
  like reusing experience. One can apply successful
  patterns to develop new software without
  reinventing new solution strategies.

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How to do that?

• Teach Java course
• Encaptulation
• Polymorphism
• Inheritance
• Go further
• Introduce a design pattern
• Give a problem
• Start with straightforward model
• Change something
• Remodeling
• solution would be one of the design patterns

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Agenda

• The motivation
• The need of introducing design patterns in the
  first year of studies
• Incorporation in the concepts of the existing OOP
  course
• Expected results

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• The idea is to learn ONE design pattern
• Starting from scratch
• Choosing interesting problem
• Discuss with the students every step of
  developing the model by putting different
  subproblems as new requirements for the model
• The model must develop with the new requirements

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1. The strategy pattern

• The idea is to guide the student through the
  process of implemeting the right Pattern Design
  to create the right OO model for the given
  problem.
• Along the way they will understand the main OO
  principles - why to develop the software in that
  particular way
• 1. Encapsulate what varies
• 2. Program to interfaces, not implementation
• 3. Favor composition over inheritance

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Simple problem

• We chose a simple problem
• To explain the students that the only thing that
  we can be certain about - is the change in every
  software development
• No matter how well one designs an appliication,
  it must grow and develop over time
• So, the first design pattern is about flexibility
  in the OO model

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Inheritance?

• To point the student that inheritance doesnt
  always work well
• Request - the behavior keeps changing across the
  subclasses, and it is not appropriate every
  subclass to have that behavior.

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The FIRST design principle

• Part of code that changes
• New requirements
• It is a behavior that should be parted from the
  rest of the code
• SO, the students should identify the aspects of
  the application that vary and separate them from
  the parts that dont change
• encapsulate it so it wont affect the rest of
  the code
• The result is
• Less unintended consequences when changing the
  code
• More flexibility in the system

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The SECOND design principle

• We introduce another design principle
• Program to an interface, not the implementation
• The different behaviors will live in a separate
  classes
• That way, the classes wont need to know any of
  the implementation details for their own behaviors

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The realization

• We will use an interface to represent each
  behavior and each implementation of the behavior
  will implement one of those interfaces.
• Program to an interface really means program to a
  supertype
• The concept of interface must not to be mixed up
  with the JAVA construct interface .
• You can program to an interface, withouth using
  the actual construct interface.
• We want to exploit polymorphism

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Another difference with the current OOP course

• We also plan to extend the knowledge of the
  students about the class relations in order to
  build more flexible models
• Discovering class relations
• Association
• Aggregation and Composition
• Inheritance(revisited)

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Has-A can be better that Is-A

• The THIRD design principle
• Instead of inheriting a certain behavior, the
  objects get their behavior by composing with the
  right behavior object.
• The students learn the third design principle
• favor composition over inheritance
• creating systems using composition provides a
  great deal of flexibility.

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Agenda

• The motivation
• To start earlier with Java (DSA will improve)
• introducing design patterns
• The need of introducing design patterns in the
  first year of studies
• Incorporation in the concepts of the existing OOP
  course
• Expected results

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Expected results of introducing JAVA and design
patterns in JAVA

• As mentioned in the motivation part
• More prepared students to embrace the higher
  level of producing OO modeling early - in their
  first OO course
• They will be ready to learn more OO design
  patterns in the latter courses
• Ready to develop OO models on their own in the
  different courses in the latter semesters.
• learning JAVA in this course will make DSA
  course more comprehendible in the third semester
• Students wouldn't have to learn the basics of
  JAVA, they will use it for simulating data
  structures covered with the course

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• Thank you for your attention