JUGS ObjectOriented Reengineering Patterns an Overview Oscar Nierstrasz

JUGS — Object-Oriented Reengineering Patterns — an Overview Oscar Nierstrasz Software Composition Group www. iam. unibe. ch/~scg/ © Oscar Nierstrasz

JUGS — Object-Oriented Reengineering Patterns What is wrong with this picture? © Oscar Nierstrasz 2

JUGS — Object-Oriented Reengineering Patterns Roadmap > Object-Oriented Legacy Systems > Reengineering patterns > Reengineering tools and techniques > Focus on Change © Oscar Nierstrasz 3

JUGS — Object-Oriented Reengineering Patterns Roadmap > Object-Oriented Legacy Systems — Software Evolution — The cost of change — The Reengineering lifecycle > Reengineering patterns > Reengineering tools and techniques > Focus on Change © Oscar Nierstrasz 4

JUGS — Object-Oriented Reengineering Patterns Lehman’s Laws Continuing change — A program that is used in a real-world environment must change, or become progressively less useful in that environment. Increasing complexity — As a program evolves, it becomes more complex, and extra resources are needed to preserve and simplify its structure. — Lehman and Belady, 1985 © Oscar Nierstrasz 5

JUGS — Object-Oriented Reengineering Patterns The Dilemma of Legacy Software A legacy system is a piece of software that: — you have inherited, and — is valuable to you. You can’t afford to throw it out, but it is too expensive to change Symptoms — — Loss of knowledge Architecture & design drift Hard to make changes … © Oscar Nierstrasz 6

JUGS — Object-Oriented Reengineering Patterns OO Legacy > Object-oriented legacy systems are successful OO systems whose architecture and design no longer respond to changing requirements © Oscar Nierstrasz 7

JUGS — Object-Oriented Reengineering Patterns The cost of change We need to reduce the cost of change over time … x 200 cost — cf. , XP Explained time © Oscar Nierstrasz time 8

JUGS — Object-Oriented Reengineering Patterns FAMOOS Case Studies Domain LOC Reengineering Goal pipeline planning user interface embedded switching mail sorting network management space mission 55, 000 60, 000 180, 000 350, 000 2, 500, 000 extract design increase flexibility improve modularity portability & scalability unbundle application identify components Different reengineering goals … but common themes and problems ! © Oscar Nierstrasz 9

JUGS — Object-Oriented Reengineering Patterns The Reengineering Life-Cycle Requirements Designs Need appropriate methods and tools Code © Oscar Nierstrasz 10

JUGS — Object-Oriented Reengineering Patterns Roadmap > Object-Oriented Legacy Systems > Reengineering patterns — Design patterns vs. process patterns — A Map of Reengineering Patterns — A whirlwind tour! > Reengineering tools and techniques > Focus on Change © Oscar Nierstrasz 11

JUGS — Object-Oriented Reengineering Patterns In software engineering, a design pattern is a general solution to a common problem in software design. A design pattern isn't a finished design that can be transformed directly into code; it is a description or template for how to solve a problem that can be used in many different situations. Reverse engineering patterns encode expertise and trade-offs in extracting design from source code, running systems and people. —Even if design documents exist, they are typically out of sync with reality. Reengineering patterns encode expertise and trade-offs in transforming legacy code to resolve problems that have emerged. —These problems are typically not apparent in original design but are due to architectural drift as requirements evolve © Oscar Nierstrasz 12

JUGS — Object-Oriented Reengineering Patterns A Map of Reengineering Patterns Tests: Your Life Insurance Detailed Model Capture Initial Understanding First Contact Setting Direction © Oscar Nierstrasz Migration Strategies Detecting Duplicated Code Redistribute Responsibilities Transform Conditionals to Polymorphism 13

JUGS — Object-Oriented Reengineering Patterns Setting Direction Set direction Where to start Agree on Maxims Maintain direction Appoint a Navigator Coordinate direction Speak to the Round Table Most Valuable First What to do Fix Problems, Not Symptoms Principles & Guidelines for Software project management especially relevant for reengineering projects © Oscar Nierstrasz What not to do If It Ain't Broke Don't Fix It How to do it Keep it Simple 14

JUGS — Object-Oriented Reengineering Patterns Most Valuable First Problem: Which problems should you focus on first? Solution: Work on aspects that are most valuable to your customer > Maximize commitment, early results; build confidence > Difficulties and hints: — — — Which stakeholder do you listen to? Vs. Fix the What measurable goal to aim for? Buggiest First? Consult change logs for high activity Play the Planning Game Wrap, refactor or rewrite? — Fix Problems, not Symptoms © Oscar Nierstrasz 15

JUGS — Object-Oriented Reengineering Patterns First Contact System experts Talk with end users Talk with developers Chat with the Maintainers Verify what you hear Feasibility assessment (one week time) Talk about it Interview during Demo Software System Read it Read about it Compile it Read All the Code Skim the Do a Mock in One Hour Documentation Installation © Oscar Nierstrasz 16

JUGS — Object-Oriented Reengineering Patterns Initial Understanding Top down Recover design Speculate about Design understand Obtain a higher-level model Analyze the Persistent Data Study the Exceptional Entities Compile it Read it Bottom up © Oscar Nierstrasz 17

JUGS — Object-Oriented Reengineering Patterns Pattern: Study the Exceptional Entities Problem — How can you quickly gain insight into complex software? Solution — Measure software entities and study the anomalous ones Steps — Use simple metrics — Visualize metrics to get an overview — Browse the code to get insight into the anomalies © Oscar Nierstrasz 18

JUGS — Object-Oriented Reengineering Patterns System Complexity View Nodes = Classes Edges = Inheritance Relationships Width = Number of Attributes Height = Number of Methods Color = Number of Lines of © Oscar Nierstrasz Width Metric Height Metric Position Metrics Color Metric 19

JUGS — Object-Oriented Reengineering Patterns Detailed Model Capture Tie Code and Questions Keep track of your understanding Expose design Expose the design & make sure it remains exposed Refactor to Understand Expose collaborations Step through the Execution Expose contracts Write Tests to Understand Look for the Contracts • • • Use Your Tools Look for Key Methods Look for Constructor Calls Look for Template/Hook Methods Look for Super Calls © Oscar Nierstrasz Expose evolution Learn from the Past 20

JUGS — Object-Oriented Reengineering Patterns Tests: Your Life Insurance Write Tests to Enable Evolution Use a Testing Framework Managing tests Grow Your Test Base Incrementally Write Tests to Understand Designing tests Record Business Test the Interface, Rules as Tests Not the Implementation • Test Fuzzy features • Test Old Bugs • Retest Persistent Problems Regression Test after Every Change © Oscar Nierstrasz Migration Strategies 21

JUGS — Object-Oriented Reengineering Patterns Migration Involve the Users Why Where to Prototype the Target Solution Always Have a Running Version Regression Test after Every Change © Oscar Nierstrasz Build Confidence How Migrate Systems Incrementally Why How Make a Bridge to the New Town Tests, your Life-Insurance Conserve Familiarity Use Profiler before Optimizing Present the Right Interface Deprecate Obsolete Interfaces Distinguish Public from Published Interfaces 22

JUGS — Object-Oriented Reengineering Patterns Detecting Duplicated Code Detect Compare Code Mechanically Understand Visualize Code as Dotplots Redistribute Responsibilities © Oscar Nierstrasz Transform Conditionals to Polymorphism 23

JUGS — Object-Oriented Reengineering Patterns Pattern: Visualize Code as Dotplots Problem — How can you effectively identify significant duplication in a complex software system? Solution — Visualize the code as a dotplot, where dots represent duplication. Steps — Normalize the source files — Compare files line-by-line — Visualize and interpret the dotplots © Oscar Nierstrasz 24

JUGS — Object-Oriented Reengineering Patterns Clone detection by string-matching Solid diagonals indicate significant duplication between or within source files. © Oscar Nierstrasz 25

JUGS — Object-Oriented Reengineering Patterns Dotplot Visualization Sample Dot Configurations: © Oscar Nierstrasz 26

JUGS — Object-Oriented Reengineering Patterns Redistribute Responsibilities Chains of data containers Monster client of data containers Split Up God Class Eliminate Navigation Code Data containers Move Behaviour Close to Data © Oscar Nierstrasz 27

JUGS — Object-Oriented Reengineering Patterns High-level refactorings make use of many lowlevel refactorings © Oscar Nierstrasz 28

JUGS — Object-Oriented Reengineering Patterns Transform Conditionals to Polymorphism Test provider type Test external attribute Test self type Transform Client Type Checks Transform Self Type Checks Transform Conditionals into Registration Test object state Test null values © Oscar Nierstrasz Introduce Null Object Factor Out Strategy Factor Out State 29

JUGS — Object-Oriented Reengineering Patterns Roadmap > Object-Oriented Legacy Systems > Reengineering patterns > Reengineering tools and techniques — MOOSE — A reengineering platform — History as an entity > Focus on Change © Oscar Nierstrasz 30

JUGS — Object-Oriented Reengineering Patterns The Components of Moose Dyna Van Hapax Mondrian . . . Code. Crawler SVN Extensible meta model CVS Model repository Smalltalk Browsing Metrics Java C++ … © Oscar Nierstrasz External Parser MSE Querying Grouping Smalltalk (VW) 31

JUGS — Object-Oriented Reengineering Patterns Moose Browser © Oscar Nierstrasz 32

JUGS — Object-Oriented Reengineering Patterns Moose visualizations © Oscar Nierstrasz 33

JUGS — Object-Oriented Reengineering Patterns Moose offers metrics and navigation © Oscar Nierstrasz 34

JUGS — Object-Oriented Reengineering Patterns Class Blueprint — Example > Root Class: —Template —Inconsistent accessor definition —Unused accessors —Direct attribute access —Template Method (DP) > Subclasses: —Siamese twins —Pure overriders © Oscar Nierstrasz 35

JUGS — Object-Oriented Reengineering Patterns Moose offers many visualizations © Oscar Nierstrasz 36

JUGS — Object-Oriented Reengineering Patterns Moose is an environment With a cast of thousands … > Refactoring engine > Static and dynamic > > > architecture recovery Trace-based feature recovery Concept mining Duplication detection Evolution analysis … © Oscar Nierstrasz Tobias Aebi Gabriela Arévalo Mihai Balint Frank Buchli Thomas Bühler Philipp Bunge Calogero Butera Marco D’Ambros Serge Demeyer Stéphane Ducasse Fredi Frank Michael Freidig Tudor Gîrba Georges Golomingi Orla Greevy David Gurtner Matthias Junker Markus Hofstetter Marc-Philippe Horvath Markus Kobe Adrian Kuhn Michele Lanza Adrian Lienhard Mircea Lungu Pietro Malorgio Michael Meyer Laura Ponisio Daniel Ratiu Tamar Richner Matthias Rieger Daniel Schweizer Mauricio Seeberger Lukas Steiger Marc Stettler Daniele Talerico Sander Tichelaar Chistoph Wysseier Ricky Wettel 41

JUGS — Object-Oriented Reengineering Patterns Roadmap > Object-Oriented Legacy Systems > Reengineering patterns > Reengineering tools and techniques > Focus on Change — Concluding remarks © Oscar Nierstrasz 42

JUGS — Object-Oriented Reengineering Patterns Object-Oriented Reengineering > Yes, there are object-oriented legacy systems too! — … which is a sign of health! > Reverse engineering and reengineering are essential activities in the lifecycle of any successful software system. — … consequently, do not consider it second class work > There is a large set of lightweight tools and techniques to help you with reengineering. — … the list is growing > Nevertheless, people must do the job! — … so pick them carefully and reward them appropriately! © Oscar Nierstrasz 43

JUGS — Object-Oriented Reengineering Patterns Trends > Software is evolving ever more rapidly — Faster, smaller hardware – leads to new application domains — Globalization – leads to new opportunities and requirements — The internet and mobile computing – raise the bar for interoperability We cannot afford to continue to develop software in the same old way! © Oscar Nierstrasz 44

JUGS — Object-Oriented Reengineering Patterns Conclusion We need to place software evolution at the centre of our software processes and tools. > Methods — Empirical research into “best practices” to support change – > Tie forward, reverse and re-engineering Tools — Model, analyse and transform evolving systems – > Co-evolution of requirements, design and code Programming Languages — Software as living systems – © Oscar Nierstrasz Context-aware programs Questions? Comments? 45